Complaining about things like Prestige skins makes no sense.
First of all, if you complain that Prestige Skins are just a recolor, don't say "Make a new skin for a champion instead". They are not taking the time and resources to create a new skin to make a Prestige one, not even close.
It's just an extra thing, and you're not forced to buy it. Do you complain about those 10k wine bottles, 300k purses or any overpriced paintings for sale? If any company can make a more luxurious product because there's demand, why can't Riot do the same if they want? It's just a smart decision.
You should be happy from Riot finding new ways to pay the employees who make it possible that League is not just a game to play, but a universe that constantly releases gorgeous art, growing lore, stories, epic ceremonies, and top quality music & videos from many genres, all of it free.
If anything, that Prestige skin can help hire someone else that might work on new skins.
Thanks,