No, why, they are useful—for pinning down enemy shooters, for example. Here, their immunity to various spells helps them a lot; and if you give them an attack artifact, they start hitting reasonably well. But then again, other second-level units fight well even without artifacts; though, of course, not all are as tough as gargoyles.
Wizards generally have big problems with the health-to-damage ratio: gargoyles (and gremlins, by the way—especially if you buy them a health artifact) have same high health and low damage; mages (at first) and (especially!) djinns have high damage and low health; golems, titans, and rakshasas have a normal ratio, but golems and rakshasas have small movement range and not the highest initiative (well, upgraded rakshasas have that "leap," although it's a pity to lose a turn).
And they are drawn coolly, am I even arguing :D?