Putting the balance point between at-will, short-rest, and long-rest classes way out at the 6-8 encounter mark.
Too few encounters, and those with the limited-but-more-powerful resources clean up. (And doing that sometimes and doing the other way at other times would be okay, but no-one ever regularly exceeds eight-encounter-days.)
Not enough or too many short rests and that whole category is borked in terms of balance vs. the other recovery models, and because of the nature of short rests when you can be doing things like riding in a wagon some modes of play will offer lots of them, while others like a sneaky infiltration where you can't waste an hour will offer none. At least this sometimes you have feast and sometimes you have famine, and as long as the DM does both it averages out. (But they don't tell a DM that.)
I like narratively to be able to use in different lengths as well as fit to player agency where they miss or take on more encounters, and if was balanced around something like 4 encounters per long rest so that sometimes I'm over, sometimes under, it would work a lot better.