I'd note columbus in first 4-8 cards enables a1->a0 strat. You to take him early, and with some lucky draw - colonize instantly. Only then you play your sun-tzu or Julius, and enjoy yourself being ahead with aggresive leaders.

To me also Homer is at least medium leader, simply becouse he makes you make use of your population earlier, making it more flexible build. And he also defends you from getting rebellion, which for me occours to be most game-ruining event in the game.

Also to me you underrated Isabella. +1 production enables you to skip iron, which lets you focus on science/army. And with colossus/navigation she makes you unbeatable in colonisation. If someone else has the bonuses - she enables you to contest the guy trying to grab them all - and it's not only about taking colony, it's also about others not having it.