Great assessment, OP. I think I mostly agree with it.
Regarding America, though, while I do think C tier is the right place currently, I do think Founding Fathers is underrated, and has the potential to make big plays. The one thing that's making Founding Fathers rather useless is the fact that Legacy Bonuses in general are rather useless, mostly because they don't build anywhere near fast enough even at double speed. There is one exception to this, however -- Oligarchy. Because of how America's bonus works, it truncates the number of turns until your next increment, so it's half rounded down. This means Oligarchy gives you a new percent every 2 turns instead of every 5, and that adds up fast. Thanks to this, you can end up with CRAZY exp bonuses late game if you went Oligarchy, and since Oligarchy helps you win your continent with its combat power bonus, you're really not sacrificing anything to get it. Unfortunately, this kinda shoehorns Teddy into Domination if you want to take advantage of Oligarchy, since none of the other bonuses really stack fast enough to matter.
However, given its potential, I think that if the devs ever decided to make the other Legacy bonuses not-awful, America would absolutely move up a tier as a result. Something to keep in mind.
Also, Teddy's home continent combat bonus isn't anywhere near as situational as you might think. It's very rare to be on a continent with no one else, and sometimes the whole landmass ends up being your home continent. Situational implies that it's only sometimes useful, but Teddy's home continent bonus is rarely not useful. Every unit is like his UU on his home continent. At the very least, he roflstomps defensive wars early game without having to tech rush anything, and can deal with barbs very flexibly.