All true, but those are big "ifs". The thing about a movie like GotG (and TWS for that matter) is that there is a confluence of events that all feed into making a great movie (or at least a very good one). Using GotG as an example....
The casting was terrific. The script was really strong. The soundtrack....well....I went around humming half of the songs for days after seeing the movie. The cinematography was better (IMO) than any other Marvel movie. It had a fresh, lighthearted feel to it and the self deprecating humor worked really, really well.
Peter Quill: There's one other name you might know me by... Star Lord.
Korath the Pursuer: ...Who?
Peter Quill: [disappointed] Star-Lord, man! The legendary outlaw? [Korath simply shrugs] Guys?
To me, that's like catching lightning in a bottle. In the follow up, I don't know if it's going to be possible to keep that fresh feel. The upside is that now that we know and like the characters, it'll be like meeting old friends. It'll almost have to be a very different movie (not a bad thing) and I'm trying to manage my expectations and just let the movie unfold on its own rather than compare it to what is maybe my favorite MCU movie.
A similar rant could be made regarding the movies TWS and CW. TWS (the person and not the movie) brought SO much to the screen and the relationship between CA and TWS was a linchpin for the movie. Keeping all of those things that fell into place for the first movies is going to be really tough and sometimes these things are out of your control.