I think it's just supposed to fix the "bug" where only warriors gain extra attacks per round from specializing in weapons. Without this, swashbucklers who specialize in a melee weapon get the +1 to hit and +2 to damage that warriors would receive, but they do not get the +1/2 attack per round.
Without mods, I think swashbucklers are the only non-warriors allowed to place more than 1 point into a weapon. (I could be forgetting a kit.) Most enemies in the game don't use the BG2 proficiency system, but they may have points in the BG1 weapon categories instead.
This component probably only applies to the BG2 proficiencies, so it wouldn't do much for enemies in the game, but it's not really doing that much for you either, so I wouldn't worry about the balance.
Edit: I think I'm thinking about a different component.
Edited by Mike1072, 04 February 2016 - 04:44 PM.