Name ONE mage that has no mobility and is meta relevant in mid-lane

Didn't think so... Mobility Creep 2018.

This is what League has become because assassins make "flashy" players with their damage that far outclasses defense in gold efficiency. There is virtually no point in building any armor at the moment and full AD teams are capable of wrecking everyone while full AP teams get penalised hard. True damage is freely available to EVERY AD champion in the game with no thoughts of the consequences.

I don't find any assassin player to be particularly impressive, their kits are designed to give a decisive advantage over many other champions so you are already playing against losing odds if you don't play these champions. How is that "impressive" when the game is already stacked so heavily in your favor? How does that even make for good viewing?

And Riot want this?

Sounds like they are trying to hard to appeal to hyperactive, flashy, self-entitled millenials, rather then honouring the core and devoted playerbase that has been with them since the beginning and long for the days where you didn't need reflexes like a Jedi to play the game.