Bruh mastery 4 is basically the same as mastery 2.
Mastery has nothing to do with your ability or familiarity with the champion. It has everything to do with how much you've played the champion.
The distinction between this is important because for a lot of people the amount of games played does not translate to their ability with the champion very well.
At the end of the day, the player's abilities at the game as a whole is the only reliable factor to look at when trying to guess who will win.
For example, most Vlad players get dicked on by Annie. But all it takes it knowing that she throws her hands in the air for .25 seconds and reacting to it to be able to pool her ult 80%+ of the time and scale against her in pretty much every match-up, yet a lot of them can't seem to do this being an OTP or not. And at the same time, Annie has to use her W to go in on Vlad, since its instant, yet most will try to start with Q or R.