It must be said that Mastery is very bugged, such that the spaceship (awarded in Information Era long before a C2C spaceship can be built), but especially culture and number of cities hugely outweigh everything else. I would also suggest that Mastery is like deactivating all other victory conditions, since you can't win by domination or culture, or any other way than Mastery (the idea of mastery is that it factors in all other victory types, but 1. it doesn't really, and 2. that's very different to having those victory types active).
I won't use it again unless it gets fixed, but knowing all its flaws, you decide whether it's for you... It does prevent a premature culture victory, which the leading AI effortlessly achieves mid-game on slower gamespeeds (and higher difficulties).