Azir - Was an awesome design, but was overloaded for pro play. Gets nerfed and gutted and has had over half of his mechanics removed.
Nidalee Rework - Turned a noob champion that could only Q spam people for 80% of their HP into a mechanical skill reliant powerfarming jungler and had animation cancels and autoattack resets removed because of being abused in pro play.
Camille - Removed her ability to clear the jungle with the E changes because she was too dominant in pro play, when the scuttle meta is what made her viable there in the first place. Her lvl 2 ganking was just a bonus.
Ornn - As soon as he was available in the shop, LCS players already knew that with that kit on release together with that powerful ultimate that he would be permapicked or permabanned. How Riot did not see that coming is beyond me.
Ryze - Easiest one to have predicted. Even without hindsight. Being able to move an entire team + minions to another location was always going to be abused by pro players.
Taliyah - Dont even need to explain this one. Shes too good in the midlane. Nerfed. Shes too good in the jungle. Nerfed. She feels borderline useless/bad to play. Give small placebo buff and now shes used to cheese botlane with Pantheon.
Aatrox - The last iteration of Aatrox finally sees some play when the meta shifted and he got some buffs. Instead of seeing him come alive for the first time in 5 years and finetuning him, they deleted the champion from the game and put the current iteration of Aatrox in. Now he sees change after change after change and the CORE mechanics of Aatrox are no longer there. Its a totally different champion.
Kalista - River vision control, constant dashing, the ability to safely remove an engaging support from a fight into the netherrealm and the ability to have her stack spears and REND baron/dragons at 2000 HP. Nobody ever saw that coming as something that could be abused. She has been trashtier for over 4 years now.
Tahm Kench - Release a fun support with new mechanics that could be used both defensivly and offensivly. Finds out later that nobody gives a damn about Toplane/Jungle Tahm Kench and only used him to keep immobile ADC's Safe from Assassins and Bruisers while running away with a turbo jet booster. Strip some mechanics away from him and BOOM you have the lowest winrate support in the game, that still gets picked or banned in pro play because of what he offers the team with the W and R.
Teleport nerfed because of proplay. Homeguards was nerfed because of pro play.
Why is this important?
Because when you design a champion, you have to think ahead. Like when Akali was reworked and she had all that healing in her kit. Did nobody ever stop and think "Hmm who can actually lane against this?". No, they did not.
Now they are changing Rakan to not be able to use W or E during his R. Because he is too good in pro play.
https://twitter.com/Squad5lol/status/1118257304233603072
Continue releasing new champions, have no foresight whatsoever, strip the champions from their mechanics and make them feel worse to play, strip some fun out of them, and then wonder 6 months later to why nobody bothers with them.
I dont want to sound like a hater of pro play, because I am not. I am a huge fan of LoL esports but if I myself dont find interrest in playing the game because of constant changes to everything, then how can I enjoy watching other people play it?
EDIT 1 : Added Kalista.
EDIT 2: Added Tahm Kench.
