The mana changes may not be that bad
Everyone is complaining about the mage mana overhaul and the argument seems to be, "mages will run out of mana instantly while adcs can just right click you for 2 billion damage without consuming resources."
And I agree with that statement but, I believe the solution is to nerf ADCs too, not un-nerf mages, because we can all agree adcs are busted right now, and there's generally too much damage in the game, I think most of us agree on that, but also, people have been complaining that mana doesn't mean anything anymore, well now it will - and it's always good to raise the skill ceiling of the game, and having to manage mana adds a level of depth to mage gameplay.
I can't really tell you to give riot some time, cause that ship has sailed, but what I'm saying is, don't be so quick to dismiss ideas that might beneficial.
TL;DR: Yes the mana change seems absurd, and it might be, unless it's part of a larger effort to re-balance resources and damage in the game.