@knobturn Gideon doesn't have a weakness (as far as "locked level cap" goes), he simply doesn't have the amazing stat gains of everyone else. The best analogy I can make is by comparing them to Pokemon. Gideon started off as a level 30 Glalie, with straight 80's across the board for stats. Not bad by any measure, but certainly not amazing. He can't evolve anymore, he's stuck as a Glalie forever. Meanwhile Ruti would be comparable to a level 1 Arceus, a Pokemon with 120's across the board. However, she's only stronger when she makes up the level differential, as is the rest of the Hero's party.
As for Sage, they're not destined necessarily to be douchebags, but the compulsions for the class make it very easy for them to be so. They're naturally egotistic and lust for power, which doesn't mean they're destined for asshattery, but couple in other personality flaws on top of the compulsions, and you get someone like Alex (or Ares, the translation switches between them for whatever reason). He wants to be seen as the smartest, most valuable member of the team, bar the hero, and he wants to marry her to restore his lineage's glory. Those are all because of his compulsion AND his terrible personality and circumstances.