I think you are substantially underestimating just how powerful that would be. The more impressive sounding traits, spells, and abilities might be 25+, but the nuts and bolts subjob abilities are almost all below that point. In quite a few cases, the difference between a normal subjob and a quarterjob would be minor. Yeah, there are some combinations where it wouldn't be a huge deal, but there are others where it can be quite absurd.