It seems to me that it's very unlikely that the vast majority of enemies will just have viscous oil, burning arrows and rock to mud/mud to rock spells lying around. Once in a while for the right enemy, sure. If it's happening to the PCs frequently, though, it's smacks of adversarial DMing to stop these spells.
That depends a lot on campaign assumptions. If a PC wizard is rare and unheard of, and most kobolds, orcs, drow, etc. have never dealt with their ilk, then, sure, they'll be green. If you imagine (as I usually do) that the party is simply one example of a relatively common archetype ("adventurers"), then many foes will be prepared to counter common strategies. In particular, one might reasonably imagine that if this particular group of PCs uses Tiny Hut (or whatever) at every opportunity, then it's likely that prior groups have thought of it too. Indeed, in the drow example, it could easily be a common spell among feuding drow, so thy may have developed tactics to deal with it.
I don't mean to dismiss your concern out of hand. It is definitely important to consider larger campaign assumptions and the intelligence of enemies. But there are ways of explaining smart foes that can be reasonable. My players certainly expect it.