Ok i dont have much time, but i ll answer to the things i remembered i disagreed.

1) In the MOBA market the last years, happens something that called monopolization. If you saw the source, it said that atm the MOBA market as a whole contains 200 million active monthly players. However, the smaller titles keep falling like flies (Dawngate, Strife, Infinite Crisis etc). At the end its likely that only Smite, Dota, LoL and HotS will remain, with LoL holding the majority of the share and Dota coming after it. So why the market has signs of saturation, the big names have still room to grow.

2) You are reffering to the IP gains as grind. It doesn work like that for everyone, not everyone sees the game competitively, especially when we are talking about LoL which has such broad audience. The newcomes, especially the ones who havent played MOBAs before, want to just check out the game and/or have fun playing it. They dont care if they have less champions than the veterans.

3)

Additionally with the burnout of veteran players, the core demographic for Riot will be the players who cannot escape the sunk cost fallacy, new players playing for free in assumption that they are getting free entertainment without any cost, or players who genuinely enjoy the game-play(I would question their sanity).

So just because you dont enjoy the gameplay, everyone who does is insane? I dont get the logic here

Veterans will always get burned out at some point. As long as theres a steady influx of new players, it wont matter. Besides, veterans can always come back (for example i stopped playing LoL for around 3 months, then came back)