I've played Forza Motorsport 5/6/7, Forza Horizon 1/2/3/4, Project Cars 1/2, F1 2017 and GT Sport (as well as many other driving games going back decades). I haven't played Assetto Corsa.
Of the above games, I'd say GTS driving physics are most like F1 2017 when comparing the race cars in GTS, in that the handling is mainly based around understeer. E.g. the Super Formula car in GTS drives quite a lot like the F1 cars in F1 2017, but the Gr.2/3/4 cars in GTS all have broadly similar understeer-oriented handling. In all these games you can make cars oversteer with too much throttle and TC off, I'm not talking about that, I'm talking about the basic driving physics. So when you play with a wheel, if you turn the wheel too far, the cars generally understeer rather than go into oversteer. When you drive the road cars in GTS, there's more oversteer in the handling, IMO not too dissimilar to how many cars handle in stock form in FM7. Some of the GTS race cars do have more oversteer in the handling, I'm just trying to make a broad comparison.
I haven't played PCars 2 all that much, partly because TBH the leaderboard functionality on consoles just plain sucks. But in terms of physics, I don't personally really see a night and day "sim" difference. It depends a heck of a lot on which car you're driving in all of these games. With some cars it certainly can be "difficult" but some cars can be "easy", and the same is true in the other games. Some describe Horizon as pure arcade, but many of the cars can be very difficult to drive in stock form, particularly in the wet, so if sim=difficult, it's as sim as PCars 2 with those cars + stock tunes.
If online racing against people is what you're interested in then IMO GTS is the best for that, partly because of the number of people actively playing it, though there seem to be fewer people playing it where you are in the US than here in EMEA region.
GTS is fine with a controller. I started with a controller, switched to a wheel, and apart from one specific car, my times were very similar with wheel and controller. After weeks of playing with a wheel, I tried the controller again, and my times were again very similar, 0.1-0.2 seconds apart for a 1:40 lap. If you do the races that have tyre wear, then some say tyre wear is much worse with a controller, but I haven't personally tested that. There are controller users who do extremely well in races with tyre wear, though.
