My beef is how one sided they all feel. Cthey should be able to branch out into other colors.
It requires flavor explanations. Jace wouldn't be all for scheming, so even though a Dimir Jace feels very Jace (milling, card draw), he still doesn't get a black mana. Ajani shifted to red because...he was pissed off. Sarkhan shifted to black because Bolas touched his mind. (Tezzeret, by contrast, was already a Starscream-type villain.) And so on.