Indeed, though the scheming that would come from that surely lowers the stability factor?
Venice was actually one of the most stable European states in the Middle Ages.
Doge of Venice isn't executive monarchy, since the doge had no real power.
Even at the end of the Republic, when the Doge's powers had been progressively reduced, that's still an over-simplification. For earlier periods it's an exaggeration, and for even earlier periods it's flat-out wrong.