It was Square's first attempt at making a more story driven game and even though they hired an actual author to pen the plot there is only so much you can do with a rudimentary knowledge of programming for the 8-bit NES so there was bound to be lots of wonky parts or story/gameplay segregation.

Leila to me is a bit of a shout-out to FFI where beating Bikke involved him mending his ways and giving you his ship. As for Leon, he's pretty badass from a concept level and statistically he is probably the best party member to join you since he's not completely useless when he joins; unlike the majority of the fourth party members barring Minwu and possibly Josef.