There was a time (about 2y ago) when I proclaimed that CIV is all about UUs, and that everything else is only from minor importance. This opinion of me doesn't have changed that much. Starting techs and traits I value a lot higher than then, because I've won with ever civ since then, but being able to rush with War Chariots or Immortals is imho still completely different from normal chariots. I have an 880 Dom standard normal, and a 1510 standard quick conquest win in the HoF, first with Hatty, 2nd with Darius. I doubt very much that I could ever have achieved something compareable without those 2 units. In the 880 domination game, I believe I rushed 3 or even 4 opponents with WCs, because they had no Ivory and WCs were just the best unit until Cuirrs. In the 2nd game, I conquered 2 opponents with Immortals, I still remember them as a lot weaker than WCs, but Darius traits are amazing for almost all games.
I wouldn't say anymore that CIV is all about UUs, but I'd still say mostly . There are nice leaders, but even though being more experienced as I played the strong ones first, I never successfully rushed with anything earlier than HAs, and those already come at least 1000y later than Chariots, if not even 1500y. At that time, Darius or Egyptians can already have and produce more and cheaper units from 10+ cities.