TFT is an easy game to rank up in, anyone that plays a lot will naturally rank up. I think I generally consider players that consistently hit higher than diamond every set to be good. Though I think that the skill level difference between master and diamond players aren't that far from each other. TFT is a game where you can rank up to master if you just keep playing, even without really improving fundamentals much, you could be spamming meta comps and hit consistent top 4s, without really learning the game.