It's true that this disadvantage can be mitigated but we should be clear. Riot does limit your play style if you choose not to pay (or grind to get certain champions).

You don't have the same pool of characters as other players who've chosen to pay for their favorite champions and this is clearly a disadvantage.

This is different from games like, say, Overwatch, where the entire hero pool is available to everyone (different game, sure but the point stands).