How to solve the mobility crisis: invisibility
I have a really good idea on how to fix the mobility creep in League: give every immobile champion invisibility. I know it sounds crazy, but hear me out. I got the idea from Lux W because it used to provide invisibility on cast.

^ These champions are outclassed and outmatched versus any mobility comp. With the mobility meta, every champion has 1000 gap closers, so it's impossible for these guys to do their jobs. Mobility used to be a very rare thing; anivia's wall was actually useful once. Nowadays, anivia's wall? NP, just jump over it with your passive
or one of your 10 other gap closers.
Here are some suggested experimental changes: Lux W (Shield) -----------------> Now gives invisibility to Lux Zyra R ---------> When she is within the radius of her ultimate, she would turn invisible (so for about a second) and her plants would turn invisible for the duration. Syndra new passive -----> Syndra will turn invisible when she is below 30% hp. This gives her the safety she needs against assassins. Malzahar ---> Really strong already so maybe just using the Q Silence Wall on himself would turn him invisible.
I think this would only work if you gave many champions invisibility similar to the mobility meta ( everyone and their mother has a gap closer). Champions with one dash used to be really powerful, but now it's a required part of a champion kit and commonplace. Instead of reworking old champion abilities to give them jumps and gap closers, give them invisibility. Every immobile champ should hav einvisibility.
TL;DR Give every immobile champion some form of invisibility to counter the mobility meta