So for those that might not understand the comparison, J S Bach was only a amazing as he was prolific. He had an incredible understanding of the rules and limitations of music during his time and how to bend them. He didn't necessarily make anything new or push the boundaries at all though. Still by exploring his chosen medium to the maximum it allowed future composers to experiment in ways that his contemporaries wouldn't be able to imagine even if they were experimental for their time.
Metroidvanias are extremely popular right now and there are some really interesting experiments happening in the space right now, but I feel like many of them are all trying to have their niche and a twist without really considering or exploring the fundamentals of the genre. Like so many of them have very linear corridors that loop to create shortcuts without giving you exploration, or they might ping-pong you back and forth between locked areas. Many take heavy inspiration from more maso-core platformers like IWTBTG or Super Meat Boy without considering how tedious that can make the getting around.
I know folks really like Hollow Knight and it has spawned many similar games, but while it does get very close, I think it still falls short of the sort of thing I'm imagining. Hollow Knight has some really incredible open "sequence design" where you're free to explore most of the world once you get the wall jump ability. It's not especially directed after that. The areas aren't really reducible to straight lines. It lets you get lost! It kinda expects you to. But it, like many modern metroidvanias, draws from the Dark Souls series and has that sort of loop moreso than say Super Metroid or SotN. It expects you to die, go back to a bench, and try again. This is fine, it's not a knock against the game broadly, but prevents it in my mind from being an example of the "J S Bach" of the genre.
The two closest games I can think of that almost fit this description are AM2R and Axiom Verge 2. The former being a fan remake of Metroid 2 is a bit rocky. Original Metroid 2 is very linear (but has incredible vibes) that means AM2R has to work around most of the time. It's a much better playing game and really does a lot with what it's based from. I would highly recommend it to anyone who is interested in the genre. Especially over the official remake, which is just mediocre. Axiom Verge 2, on the other hand, is a more focused sequel to a game that was trying to do a bit too much all at once. It refines a lot of stuff, while sticking true to a lot of genre conventions (even if it has it's own twists on them). I should really replay it at some point.
I don't really have an ending to this. I don't really want to go into the specifics of what I would think a J S Bach of Metroidvanias would even look like. It's mostly musings. I don't think I'll ever make a game that could be considered the J S Bach of anything, but it is an aspiration if not a concrete goal. Now, it probably should be pointing out that Bach did die in relative obscurity (though still quite well off) and wasn't really widely known as he is now until well after his death, so maybe this game already exists and I just have yet to find it.