But this isnt matter of effectivity ...
Just as with Racial Ability Score bonuses, just as with Bard proficiencies, just as ... well, everything in the game.

We want to pick it oureself, no matter how good or bad it will be!
Just imagine that Larian would simply decide that all Fighters will only wear Greatswords, bcs they "seems to be best" ... and you would loose option to wield any other weapon!
That would suck right?