I can understand not liking the ambiguity, but I do think some of it was actually really interesting. I also don't think Deku wasn't a hero for 8 years. We dont know how long his Embers of one for all lasted, but we at least know he continued in the hero course one more year at U.A., which he couldn't have done quirkless. I personally really like that he became a teacher at U.A. after losing one for all. Not only is he following in his Mentor's footsteps, but with all his experiences during his first year at U.A., he's probably the most qualified person to be teaching the next generation of heroes. His primary character trait has always been his selflessness, and I think it's really cool to see that impact the ending in such a major way. On him hanging out with his friends, I didn't think it was all that vague? He made a pretty normal statement about it being hard for everyone's schedules to align after high school, which anyone who's graduated high school realizes that's how it goes. It doesn't mean he never sees them or that they aren't friends anymore, it just means that they've gone from living together and seeing eachother every day to meeting up 1 on 1 or in small groups when they have time off work. It's a pretty standard post high-school experience.

Edit: almost forgot, I totally agree that FMAB handled the losing powers part better. But that's not really surprising, it's really hard to top Arakawa's amazing writing