Exactly. Use the right tool for the right job. It's not meant for hitting 1-2 big bags of hit points, it's meant for quickly clearing the room of minions...and it's amazing for that.
One of the issues, I think, is that this runs up against how a lot of DMs design their combats.
- I am probably only going to have like 1-2 encounters before the party does a long rest, I better make them DEADLY!
- OK, I've got this XP budget to spend on monsters. What's the deadliest monster I can get for that budget?
- Example: At level 5, your high XP budget is 4,400 for a party of 4; DMG recommends not using creatures with a CR higher than the party's level, so for CR 5 we've got two CR 5 creatures and 800 xp leftover.
- OK, great, I've got a deadly monster, and some left over XP, what's the deadliest companion I can get for that monster? for the example, that gives us one CR 3 creature.
- A hard fight with 3 creatures, sounds manageable, that's the fight.
Anyone who brings
Fireball into that setup is not going to drop anything. 28 points of damage won't even halve the hp of the CR 3 critter. And if I make most of my encounters like this....that fireball never gets to shine. Action denial against one of the CR 5 creatures is
definitely the better play, since even a reprieve from 1 round of attacks is significant breathing room.
If I try to make a hard encounter with CR 1 monsters, I'm looking at, say, 8 of 'em for only 1,600 XP and then I've got an encounter at the end of the day with probably 10-12 monsters, a headache to run, and those 8 CR 1 creatures only stick around for a round or two anyway. Bah, not worth the time in a lot of cases.
Any spell designed to nuke minions runs up against the fact that minions are a
hassle in 5e. Not that it never happens, but, like, if I'm going to spend an hour of playtime in a fight, I'm going to want to not waste that time on transactional lil' guys that boof the moment someone sneezes hard.