It's worse than that. The cables are done too.
Most houses are wired with Romex (NM) cable. That's not rated for getting wet. It has paper packing inside the sheath that just wicks water like crazy.
If the people who built the house were flood savvy, they built with UF cable, which is wet-rated and notably does not have that paper packing. It will be fine. Or they built with conduit and use THWN or THWN-2 individual wires. Those are also wet-rated and work fine even if the conduit is full of water, which is the normal expectation outdoors.
All the switches and outlets are done
Flood damage destroys everything, becuase it's not just water, it's a lot of crud too. Flood cars are finished. Some of that crud is electrically conductive, and it has gunked up each of the receptacles with it. Also, the crud is corrosive, so anything in that receptacle that could corrode, is right now.
For all those reasons (electronics are extra sensitive to corrosion), the GFCIs are all finished and must be replaced.
The service panel is also done
Service panels, even outdoor rated ones, are not rated to go for a swim. The crud is also inside the breakers laying conductive tracks and doing corrosion damage. These breakers will no longer be reliable. It might be possible to pull the buses out of the service panel and clean them, you'd have to see.
If you look at news footage of Houston's recent flood, you see lots of 2-storey apartments, 1st floors flooded out, and 2nd floors with the lights on and the A/C running. Flood-savvy builders take their power from overhead lines not underground, and put the service panel on the 2nd floor. They put 1st floor circuits on GFCI breakers so they don't electrify the water and drown people. A GFCI breaker protects the entire circuit and makes GFCI receptacles unnecessary.
All GFCI devices can protect downline loads if wired correctly. You are correct that a GFCI receptacle on the end of a circuit is a bit of a waste.
(Usually) you can't work on rental properties
Most areas have a law that only licensed electricians can do work on rental properties. That is to prevent landlords from doing shoddy work on the cheap and killing their tenants.
Check with your local authority (the department in City Hall you go to pull permits). They will tell you what a handyman can and cannot do with electrical in rental units. If they allow you to do anything at all, it would be limited to changing receptacles, switches or lights. GFCI receptacle changes could be included in that.