In all fairness, Blue Magic in FF games does tend to both be ridiculously powerful and absolutely horrible at the same time. On the one hand, you can get access to some of the nastier abilities monsters use. On the other hand, it often requires you to deal with one or more of the following:

1. Get hit by the ability and survive the fight just for a random chance to learn the ability
2. Have the blue mage leave the party for a random length of time while they learn the ability (I'm looking at you Gau!)
3. Give up all control over the blue mage while they are using the ability (Gau, Gogo, and Mog from FFVI spring to mind off the top of my head for this)
4. It's only usable as a Limit Break, and there's so many better ones (as well as characters better suited for that char's main role in the party)

To make matters worse, the blue mage is often the worst party member of an ensemble cast in Final Fantasy games despite their potential power. Or maybe it's done as a way to balance their potential power. Either way, for decades the Blue Mage has been regarded as bad. And unlike red mages, the blue mage doesn't even have versatility as a claim to fame.