Wait. You're planning To DIY a main panel replacement???
And you don't like meter-mains?
That doesn't make any -- um, just read on.
TLDR: don't merely get a meter-main, get a Ranch Panel and a nice big'un. Solar-ready if you're into that sort of thing lol. I would pay to replace the meter with that, and tell them to leave the main panel alone. Then, I'd DIY the main panel. Because that's relatively easy/dumb make-work with little risk, which is why the electrician is so "on fire" to do that work and not any other.
What are some real-world devices available for purchase that would satisfy this code requirement for exterior disconnect? Examples of different types of products/solutions rated for 200A would be very helpful.
A meter-main, a plain old disconnect switch, or a main breaker in a box. Price the various options if you want to, but the "meter main" is generally the cheapest if you're replacing your meter pan anyway. Which you will need to do, in order to exploit 200A service.
When NEC says "disconnect", in practical terms they mean "main breaker" because a breaker is a disconnect and it would be money-wasteful to have a discrete disconnect and also breaker.
And having multiple enclosures is not only costly, it's ugly too - so a single "meter+main" enclosure becomes a cost and aesthetics optimization.
That's why NEC says "disconnect" but everyone says "meter-main".
Another rather useful thing for many people is the "Ranch Panel", which takes the meter-main and adds 4-12 breaker spaces. Just like that, things like solar, generator/interlock, surge suppressor, shed feeder and EV charging become easier.
Now with the Ranch Panel, a future panel can be fed 200A off the "thru lugs". However a legacy 60-125A panel and its feed wires can be fed from a same-size branch circuit breaker. This removes the urgency from replacing a panel that isn't actually dangerous or broken. The Ranch Panel's main breaker can also be swapped for a 100-125A main to match the existing service size; at that point you can freely fill it with whatever.
For what it's worth, AFCIs don't need to be breakers; they can be AFCI receptacles or deadfronts at the first outlet. However I prefer to run EMT metal conduit to 4-11/16" square boxes (for the space) near the panel, and mount dual AFCIs there. That qualifies for the standards for entirely new work, since the run from panel to first outlet is inside metal conduit. It's also easy to wire since the AFCI-protected hot+neutral can simply use the same conduit to go back into the panel and tie to the circuit hot/neutral.
If I used a combo meter main panel outside, would that designate my "main" panel inside as a sub-panel? What if I used a disconnect switch instead?
The former "main" becomes a subpanel in all cases. The main panel is the first disconnect past the meter.
There are also solar-ready meter-mains which provide a separate utility-side breaker for solar. This removes all amp limits on the size of the solar system.
Does the code not require me to install this disconnect if I can reuse my meter base (i.e. if it's already 200A rated)? If I don't do it now, would I then have to if I later replaced my buried cable?
The triggering event will definitely be if you had to replace your meter pan for other reasons. Whether it's required as a main panel upgrade is up to the AHJ. I would expect the requirement to land if you are doing something more than a straight repair of a broken pan, and if you are disturbing the meter pan in a way the power company must de-energize the pan for service. A panel replacement wouldn't qualify, since the power company can simply pull the meter for that. It's really up to the AHJ.
But why on earth would you resist a meter-main if you are doing DIY replacement of the main panel? What do you think they're going to do, let you work "live" or that work+inspection+hookup can happen in a day with no snags or gotchas? You are better off installing a meter-main-ish-sort-of-thing like a Ranch Panel, as a single one-shot operation, probably for hire... get re-energized, and then you're now in a great position to DIY panel replacement.
Not least, think about how this changes the panel replacement task. Before, it was a panel upgrade, which definitely needs the full rigmarole of permits and inspections. But now, it's not an upgrade - it's a REPAIR. Remember, it stopped being a "Rule of Six" panel the moment it got fed from a 125A breaker elsewhere. Now, it's just a random main-lug panel. And you are replacing it in-kind with another main-lug panel. Well, that's a repair. There's nothing to permit there.
Sure, it's a 225A-bussed main-lug panel, but 125A-bussed panels were not available and nobody really cares. Sure, it's 40 spaces instead of 14, but you're not adding any circuits so it doesn't matter.
Or if there was "no sale" on that idea, I would propose adding a Critical Loads subpanel in a position where existing wires will reach, and say "I want to move some critical loads to that panel". Now you're only messing with a few circuits in the house, so you're not taking your entire house down for the duration.
You have a split-bus panel with fatal defects
Split-bus panels operate under the Rule of Six, using an internal subpanel. Rule of Six means that there is a "main breaker" area with up to 6 "main breakers". This area cannot be de-energized. Further, nothing prevents this area from overloading, which means these panels are vulnerable to being overloaded when people do "upgrades" without re-calculating their NEC Article 220 Load Calculation.
This doesn't call for replacement, but it does need to have a main breaker in front of it to eliminate the "overload vulnerability". Meter-mains do a fine job of that.
However yours has 2 additional problems. #1 it's an ancient GE panel, for which availability of full-size breakers is hit-and-miss. (though you can get thins all day). #2 you mentioned a faulty lug that cannot be torqued - that is an instant deal-killer. Right now I would remove those un-torque-able wires and feed the Lighting Area with a backfeed breaker, condensing circuits as needed to make it fit. The risk of arcing and fire is severe. Torque matters.
How I would stage the work
I would actually break it into three mini-projects.
The whole point of this is to "box in" project 2 so it is the smallest and simplest project it can be - to maximize the chance of getting it done in 1 morning, so the inspector will be confident you will be powered back up same day and won't have to ask uncomfortable questions about where you'll be sleeping the night (inspectors do not like people being in power-out houses). Whole panel swaps are hard, especially for DIYers, with many complications. By giving you the power to DIY shutoff the panel without power company intervention, it "sets you up for success" on project 3, the actual panel swap.
Project 1: Add a ground bar to the old panel, separate neutrals and grounds in that panel, and run a separate ground wire parallel to the service entrance wire (from panel to meter).
Project 2: Replace the old meter pan with a meter-main (full stop). This will involve full permits and power company intervention. Removing the old service drop, the house will be down for the duration, and then getting inspection/approval and then the power company turns the power back on. However, because it's a small project, there's much less to go wrong so you are less likely to have a protracted "power out" situation. I'm deliberately excluding the main panel swap from this, because that would make things much more complicated, especially given all the surprises you can find in a main panel swap.
But a meter-main isn't mandatory! Why should I do something that isn't mandatory? Because it allows you to break the project into smaller, simpler, more achievable bite-sized projects, thus making it all easier and increasing the chance of DIY success.
Now, you actually could go "above and beyond" on this in a couple of ways. #1 instead of a straight meter-main you could use a "Ranch Panel", which adds 8 breaker spaces to the meter-main. This could do things like allow you to feed the old main panel 100A while building a new main panel right next to it that is fed 200A. Then you can move circuits from the old to new panel 1 at a time at your leisure, if that would help your workflow. Or the 8 breaker spaces could accommodate generator interlock, solar, surge suppressor, you name it. #2 you could install a 400A meter-main, which includes a 200A breaker and a blank space for a second 200A breaker (to feed a second 200A panel - that is the normal way 400A services are done). Even if you're not buying 400A service today, the meter-main is ready to go the day you upgrade. And they make 400A ranch panels too.
Project 3: (if needed) replace the former main panel (now main subpanel) with a better quality of main subpanel. Because of project 2, the power company is NOT involved and this gives you maximum flexibility/choice on how to approach it. For instance you could leave the old panel in place and add a new panel next to it. Move circuits over 1 at a time at your leisure, then scrap out the old panel at your leisure.