They absolutely do change this all the time - session limits vary wildly. The most damning proof of this is that there's absolutely no information about how many tokens you get per session with each subscription level, it's just terms like 5x, 20x. But 5x what? Who knows?
That's not proof of anything. Also the usage is not solely based on tokens because you also have to factor in things like prompt caching costs (and savings). So it's based on the actual API cost.
Again, it is not based on number of tokens. If it was solely based on number of tokens then things like cache misses would not impact the usage so much. It's based on the actual cost which includes things like the caching costs.