that's why there was things called espers that could raise your stats upon leveling up as long as they were equipped just keep sabin low level and raise his int & str as needed.
but yea, i still rather enjoyed locke, and really if you abused the psycho cyan glitch, cyan wasn't too bad either, but i just enjoy the retort skill lol.
To be perfectly honest I only didn't use Terra over Celes cause the game is too easy if you use her and her morph ability. I admit to Terra overall being stronger than Celes in the later parts of the game in World of Ruin. Btw, Relm has an amazing int score, its my biggest reason for using her.