For me the biggest negative to F2P is in competitive games, so especially Rocket League in this case, because being F2P means that the competitive element and matchmaking system is 100% worthless.
League of Legends is the most popular competitive game in the world, and is free to play. Calling the competitive aspect and matchmaking worthless in f2p games is incredibly naive.
My experience of two games going free to play, PUBG and Rocket League, is that in the former 100% of games now have cheaters in and in the latter ~25-40% games have people playing on fresh accounts to keep their rank artificially low.
Haven't played either, but I can tell you that cheating is exceedingly rare in League and that their ranking system does a good job of figuring out if a new account is from an experienced player or a legitimately fresh face. By the time you've played 10 games you are given a reasonably good matchmaking experience. Perhaps that's why League is so much more popular than PUBG and Rocket League?