My main experience with "Pay to Play" games has been Hockey Ultimate team and EASHL in the NHL series so I'll just talk about that...
I'll preface this by saying that I've been playing HUT from the beginning (NHL 11) until NHL 16. I was never not in either Division 1 or 2 for the majority of the time I played. I spent hours working the market and I also bought packs with real money like a total chump (I think i spent close to $300 on packs one year).
In regards to HUT it isn't just that people can purchase packs with real money, since we've been able to do that since day 1 in NHL 11, it's that (at least in NHL 16 and 17) there have been major complaints that there isn't enough disparity in attribute effectiveness for players (Little to no difference between say, an 85 OVR Valterri Filpulla and a 90 OVR Duchene, for example) and you don't see a real difference in player effectiveness until you get these legend cards, TOTW cards, special cards, etc...which are EXTREMELY difficult to get just from opening packs. You have to either grind out pucks in the market (which takes a big commitment) or invest a lot of money. So when you couple that with EA's apparently now confirmed manipulation of games through momentum it makes for an artificial competitive experience where people can pour hundreds of dollars into getting collectibles and completing sets so they have super teams that are very difficult to beat when you get into the top 3 Divisions.
HUT gives you "increased chances of rare Gold Cards" in certain packs but those rares were a lot of the times just stock players in the 87-90 OVR range and they had a double-sided problem with them. They were not only nowhere near as effective as the Hero/Special cards, they were insanely similar to the player cards in the lower overall tiers (83-86) range where most players fell into. So I could grind away for weeks, playing games, working the market, and building a team full of high-80's players on it, which I actually liked doing as it was part of the fun of building my team, but then when you get into actually competitive divisions (DIV 1-3) you start going up against players with a lot of skill and a lot of great players.
Originally in the first few years of HUT this wasn't that bad of an issue. You really could beat teams that were better than yours by playing better than your opponent. Now, however, with dynamic difficulty/ice-tilt/momentum/etc...the outcome of the game is less and less in your hands and beating teams full of Bucyk's and Bure's that people built by spending money on packs is a lot more difficult. You have to beat a superior team built with real money AND beat EA's dynamic difficulty.
THIS is "Pay to Play". It sucks. The competition is this inflated mess where you absolutely must have the best players just to have a chance to overcome the randomness EA throws at you.