The thing that makes this illogical to me is that once you reach basic fluency, you stop needing to study since you will now be automatically improving your language skills every time you hold a conversation, read a newspaper, watch a television program, etc. It's genuinely just the relatively small initial hurdle towards ~B1 that is a slog, but after that, you never have to actively study again if you don't want to.

It doesn't feel like that for me. I reached professionally assessed B1 in French about 6 years ago and I don't feel I've reached B2 yet.