So what's our assumption here? A feat-less game that also bans Multiclassing (where Str 13 is required for Paladin and Barb?).
Nope. Any situation where the Str-based character doesn't pick up one or two specific feats.
IME featless games are very rare, but characters not picking up GWM are not.
. . .So Finesse weapons are only a problem:
1) In featless games with no multiclassing, in which case it amounts to (at best) a minor if indeed any benefit to fighters, and a net loss to Paladins and Barbarians.
Are you assuming that all Str-based characters take GWM? I feel that there is a disconnect here.