Is there an alternative that is better suited to this need?
Yes, it's called a tap. They're installed in all your sinks and showers/tubs.
At the lowest point of the plumbing you can access, install a new T connector, then off of this T, install a valve of some sort. When you want to drain the pipes, instead of disconnecting the plumbing, all you have to do is open this valve. Gravity will help you by forcing all the water above the valve downhill and through the valve.
You could get fancy and make this new valve a garden hose bibb. This will have a threaded end onto which you can thread a garden hose to aim the water to some convenient location for disposal (or, simply, into a bucket) instead of just allowing it to flow onto the floor.
I have no confidence that the water will drain enough and out of all parts so that it won't damage when frozen solid. ... or am I worrying too much?
You're worrying too much.
Take two store-bought bottles of water. Put one, unopened, directly in the freezer. With the other one, open it, take two swallows of water, cap it tightly, then put it in the freezer next to the other one. Come back in 24 hours and see what's happened. The unopened one will be swollen to its extreme, possibly even ruptured. The one with two swallows might have forced some of the concavity out of the bottom of the bottle, but probably not.
It's not like you're running a pipe cleaner with a rag through your pipes now, getting them completely dry. So long as the water/ice has someplace to go as it freezes and expands, it'll be just fine. The problem with freezing happens when a fully pressurized system freezes up. All the pipes are already full of water, so as the ice expands it has nowhere to go but out. With metal pipes it's about a 99.999% chance of a pipe burst. With PEX, the pipe can stretch and, when the ice melts, the pipe will return to its original shape. PEX can take this many times before it actually bursts.
As some other answers & comments have noted, drain some of the water from the heater. The pressure tank will be fine as the ice can expand into where the air normally goes. The pump will drain enough that ice can expand to where the water normally goes.
I'm not certain about the water in the softener's resin tank. I would think that if it were to freeze, but the plumbing into and out of the softener is open (i.e. there are empty pipes) then the ice should be able to expand into those pipes. However, I'd suggest contacting the manufacturer to see if they have recommendations on winterizing it.