>>45591339I don't think anyone for sure knows what fuckass rating system Niantic uses, but the assumption is it's an ELO system.
Season 6, like Season 4, has a mix of straight "Win X to rank-up" with no risk for losses other than wasted time. The top ranks are rating based, and generally 3 wins and up gets you a rating gain while 2 wins and lower gets you a rating loss, with more rating changes equivalent to distance from the median. (3-2 is about 10+ rating, 2-3 is about 10- rating, 5-0 can be upwards of 60+ rating and 0-5 can be the same in reverse)
Pic related is Season 6's ranking system.