I would heavily disagree. LoL now practically throws champions and skins at you now with some of their currency systems. I think the other thing is that you don't need all the champions unlocked to be good. You would probably do better by choosing a set couple of champs and getting good at those. Yes, meta's change, but that is on top of good mechanics. LoL is a lot of things, but I would strongly argue against pay to win.

LoL is a game that rewards learning deep, not wide. You won't win just because you have access to many champions. You will lose, because you don't know how to play those champions, and will never learn how, because you are always starting over with a new one. Counterpicking and tier lists are lies that scrubs tell themselves to feel better about their lack of basic skills. You need 1 champion you can play perfectly without error, and a couple backups in case you don't get to play that 1 champion.

At 1 game a day, it will take you far longer than 9.5 years to learn to play every champion in the game, so it is irrelevant how long it would take to get all of them. You could play more than 300 hours on a single character before it would benefit you to add a second one.

But you're not paying to win. You're just paying to have a different experience. In fact, when you start your best shot at winning is with the champions they give you, since they're the easiest. League is better described as pay to lose if anything.