What are the bronze to diamond levels in the rankings?

Your rating is how good we think you are, and your level comes from it: bronze below 1,600, silver from 1,600, gold from 1,700, platinum from 1,800, diamond from 1,950.

Diamond also needs at least 30 matches, so nobody gets there on a lucky run.

While you're still settling, you don't have a level yet. And missing a month doesn't cost you a level: you lose points on the leaderboard, but your rating, and so your level, stays where it is.