But hypnotic pattern isn't a bard only spell...
Neither is
fireball a wizard-only spell. Sorcerers have native access to it, and warlocks and clerics can get it if they have the right subclass (and druids can get
lightning bolt the same way).
(As an aside, how does it compare to fear?)
I would argue mostly poorly.
*
Fear is a 30 ft cone,
hypnotic pattern a 30 ft cube with 120 ft range.
*
Fear makes its targets frightened,
hypnotic pattern makes them charmed. I'm not sure, but I think resistances to fear are more common than resistances to charm.
*
Hypnotic pattern makes foes docile. They stand around doing nothing, waiting to be picked off at your convenience.
Fear on the other hand makes them run away, which in a dungeon setting will often lead to them warning other inhabitants.
* Once out of sight, the subjects of
fear get new saves every round to break the effect.
Fear does have one advantage in a situation where there aren't other foes around to be warned: it moves the subject away from you. That means that even after the spell is over, it will take a while for the subject to get back into the fight.