Speed to win is not our chief criteria, 'ease' and 'smoothness' are, however nebulous they might seem. In any case, early aggression is very strong, and all of the civs you listed rate very highly by our standards.
I'm not ready to throw every VC out in favor of Domination. The best civs will have multiple options open to them, and the good news with conquest is that it can play into any victory type. Russia receives big boosts to religion and culture, as well as a nice land boost to get every city off to a nice start. That bonus is pretty similar to Rome's – where Rome gets a free monument, Russian cities simply don't need one. Rome does get the bonus culture, but Peter can easily get that via trade routes. And, of course, religion can be very useful for midgame conquests. That's why Russia rates B Tier in my book.
As for Japan, I'm still mulling them over. Their district boosts are very nice. Their combat bonus is solid, but situational. Adjacency bonuses seem overrated, and theri UB is unimpressive. They might fall a tier, to be honest.
I'm glad you brought up Saladin. Alongside the Russians and the Greeks, the Arabs are one of the most faith-capable civs at Deity-level. But where Peter excels at culture, Saladin excels at science. They both seem very capable, and in both cases, religion opens up a toolbox that isn't open to other civs without a lot of effort.
