3rd-5th level spells are real good, and warlock doesn't get lower level slots,
This means hex is pretty niche. I wouldn't say useless, as it can come up over multiple fights pretty regularly,* but most of the time you will have something better to do from hypnotic pattern to a summon to counterspelling to fireball spam. Hex is when you have a slot to use and not much better stuff to use it for. Kinda like bless in all honesty, it is not big but it is something, and something is better than nothing.



*hot take, if you are taking fire to break concentration on hex, your winning.