I often get the feeling that the designers thought short rests were fairly easy to get, so they overvalued abilities you recover on a short rest. Had a short rest been like in 4e, about 5 minutes long, the warlock recovering their spells on a short rest would have been amazing. But instead, at least in the game I'm running (Princes of the Apocalypse, so fairly dungeon-heavy) it seems like the number of situations where the PCs could take a short rest but not a long rest is fairly small.
That does seem to be the more common (though not exclusive) play experience.
The assumption is two short rests a day.
It really makes me wonder how a house rule that all "recharge on short rest" abilities are multiplied by three and recharge on a long rest instead would work. Has anyone actually played with something like that? I'm sure it would be a bit uneven, but the disparity between long rest and short rest classes is probably my biggest complaint about 5e at this point.