From what I've heard in FF2 it's near impossible to get 16 weapon skills, but there is an even sneakier trick where you can train with one lower skill, then change your equipped weapon before the end of the battle, and the currently equipped weapon will gain the full experience rather than the other one. So for example if you had staves at level 1, and swords at level 10, and you gain enough stave experience to get a level, and then switched to a sword before the battle ended, then you'd gain the level in sword rather than staves.

Very cheap, and not something I'd do. I'll stick to beating up flans.