I disagree that it's a waste to teach anyone magic. In the first place, you might as well teach everyone some magic because they won't gain stats at level up without an esper equipped. Secondly, it's definitely good to have healing spells with everyone even if you're going to use their special skills for attacking. Also, I would argue that the delay on Cyan's ability makes it significantly worse than magic. Sabin's abilities are probably comparable to magic but only if you're good enough to have basically 100% success rate on the inputs which I never was except the easiest ones that had no continual motion. The deficiencies of the weaker magic users are quickly offset by equipping the right espers. Sure you can lean into their strengths to differentiate, but that's true of most of the games that came after FFVI as well. I can just as well give unique materia setups to each character (and usually do at some level) focus on magic junctions for some characters and strength junctions for others, etc. Heck FFVI even includes a character that can equip other characters' abilities so even those aren't truly unique.

No argument that Terra's trance makes her the strongest, but that applies across board, not just to magic, and I think makes her the best candidate for Genji Glove +Offering combo. You've got me on Strago because some Blue Magic can be pretty good but I never used him much and generally found learning Blue Magic to be a pain because he always seemed to die on me when I was trying to learn something.