Tryndamere in a bad state and never played in competitive and very rarely in SoloQ - gets nerfed beacause AP was played a little and AD Trynda got hit hard by increasing CD on his E. Gets a buff patches later on his base damage. HUH? What about his only escape that you hard nerfed?
Tanks were meta 4,5 seasons - get nerfed at beginning of S8 in order to end the tank meta, just few months later they get buffed again and are already largely played. HUH? Why? read bellow
Bruissers didn't have a keystone to fight tanks few months into the season 8 and were heavily abused by them until they got Conqueror, Conqueror was hard nerfed just few months after it's release and with tanks getting a buff in a meantime it only meant tanks are back in the meta.
Mages were hard nerfed in terms of their items, mana regen and doran ring. Few months later their items are slowly becoming overloaded with actives,passives,damage etc just because Riot doesn't know how to deal with it so they just add things up.
Asssassins were hard nerfed and reworked with Riot saying 'they are just unhealthy for the game and shouldnt one shot you' (literal quote from them, check it). Few months later LeBlanc is reworked and dominating again, Duskblade buffed meanwhile bringing Assassins back a little, Akali reworked and made OP, most importantly after saying assassins are unhealthy, Riot released Zoe and Kayne, champions that can one shot you while not even showing on your screen or without beeing on a map (Kayn).
Adc were unhealthy with their shielding supports and Ardent Meta, instead of hard nerfing shields and reworking certain champions (Lulu) because no matter what their kit will always be strong, they kept on gutting Adc's leaving them with no spot on the rift after Riot finally lost their minds and hard nerfed their items.
Jungle was in more than alright state so Riot hard nerfed their pathings and early pressure, after nerfing literally all lanes it made junglers op again since they are the only one that could give game breaking pressure and presence.