Final Fantasy VI Turned 25.

[Rez09]

I don't think his point is so much that teaching people magic is a waste, but more that it is a powerful mechanic that overshadows unique character traits and so characters in the game appear far less defined and diverse than they actually are when you invest in it. It's never that different characters don't have unique options to offer, but more that the generic catch all they share is almost unarguably stronger than what they do bring, barring unique cases like Gau. Or so goes my interpretation.

That said, I find characters in this game really shine if you are willing to play at a relatively low level or without espers, as most of the cast have unique traits that make them ideal for certain tasks, with only Shadow and Gau being oddballs that are good at basically everything. It's a shame you have to kneecap yourself for the experience, but I'd argue it is worth trying out at least once.