Riot lack of attention for details is going to be it's downfall.
Say what you want about the balance team, but at least they keep the game fresh and ever changing, even if it means we have 4+ 55% win rate champions, at least you can be damn sure that the matchs you are playing today are never going to be the same as the matches you gonna be playing 3 patches down do road.
And most of they new champions are fun and healthy to the game (Expect CertanlityT ones)
So no, balance it's not what makes this game unenjoyable for some people.
No, it's Riot lack of attention for those tiny little things people have been asking for 6 years yet never deliver.
Champions that have been waiting for a rework since day one, yet they rework Skarner once again, and rework Garen for somereason, yet Yorick/Taric/Poppy are still waiting for their reworks.
Sandbox mode, something that many people would love to have to practice, and some others to create content for their Twitch/YouTube channel, is not going to happen because they dont want people to "grind" it, yet runes are a still a thing.
Champ select report, so we can do something about the occasional (and not so occasional) champ select troll, right now "good" players cant do anything about "bad" players, the best they can do is report after 20+ of toxicity and hope they dont see them again, but even if they do, getting a new Acc is super easy, hell you can even buy some lvl 30 acc for something like 20 bucks.
Replays, in game Voice Chat, the ability to move rune pages around, and some that I forget right now.
Honestly, some of them are really easy to implement, such as moving rune pages, and some others need to be implemented carefully since they have some negative sides that need to be taken care of, such as Champ select report/Voice Chat. But there is no reason for sucha suscceful gaming company not to have done this before.
It's not like this game just started, no, it's been rolling for 6 years now, and made a huge amount of money, yet simple things that shouldnt cost more than a few houndred dollars are nowhere to be seen in game.
And that is going to be it's eventual downfall. People will migrate to better games, and will eventually forget about LoL and all it's flaws because they found an other game, though flawled too (they all are), at least some of the most basic things are there to make the experience more enjoyable.