Good points
@Antony Snook, but an American breaking into a top tier team? Highly unlikely as we have seen drivers like Lewis, Lando and George Russell that signed onto mega names when they were mere children.
As far as an American in F1 the lack of commitment from Michael Andretti was his downfall. Yes the car wasn't supposed to be competitive , and Ayrton Senna was...well Ayrton did manage to make it work. Back then testing was incredibly more relaxed than today's F1 and simulators weren't really a thing then so Andretti did himself, and the team a disservice by not being their as much as he could have.
Having said that the best opportunity for an American in F1, as I see it, is Andretti Autosport. Now if all this should happen Sauber/Alfa haven't had a whole lot of success and unless a change in ownership (again) does the trick the best case scenario is for someone like Colton Herta, a lower Formula driver or a second go around for Rossi would be to show their capabilities and sign elsewhere in a couple of years.
Still a possibility at this time, but hope it works out better than the USF1 effort, or lack thereof, and the current embarrassment that is Haas.
Edit: well that dream went to hell in a hurry.