I'm a fan of single player RPGs. FO1 was a single player RPG. FO2 was a single player RPG. FO3 was a single player RPG. FNV was a single player RPG. FO4 was a shooter.
FO4 wasn't progress. Progress is when you take what came before and make it better. Instead, they tossed out everything that came before and replaced it with a brain-dead shooter. They didn't make it better. They made it different. FO4 lacks the humor of the Fallout series. FO4 lacks the interesting quests of the Fallout series. FO4 lacks the depth of the Fallout series. If you take out everything good, that's not progress.
That doesn't mean that FO4 is a bad game, but it's not Fallout. Not really.
From what I've seen of the leaks, Vault 76 is just a rust clone. That's not making Fallout better either. That's just taking Rust and slapping a Vault-Tec uniform on it. If I wanted to play Rust, I would play Rust. I don't want to play Rust. I want to play Fallout.
After the backlash from long-term fans like me over FO4 and its change from an RPG to a shooter, I was really hoping that Bethesda would return Fallout to its roots so that they could recapture the existing fans like me who are just about fed up with the series at this point. Instead, it looks like Bethesda went off in a different direction entirely.
This is what makes me think that Bethesda doesn't have a clue what Fallout was all about. They aren't even making games of the same genre.
If you took Sonic the Hedgehog and slapped a Vault-Tec uniform on him and had him collect caps instead of rings, nobody would say that was a true Fallout game. They would say it's a Sonic game. FO4 was a shooter, and Vault 76 looks like Rust with a Vault-Tec uniform slapped on it. They might be fun games for some, but they aren't Fallout.
To take your band analogy, while it is certainly true that bands need to grow to survive, we're not talking about growth here. We're talking more about something like the Beatles suddenly ditching John and Paul and replacing them with Taylor Swift and having them all start playing country music. Some folks might actually like that, but if you are a hard core Beatles fan, it's not going to be what you want to hear. It's not progress. It's change.