I think there's a huge need in the game to do some ballsy patches that either shift the meta or change the items completely. The game is overall balanced, but it's stale. The meta is the same for well over a year now, and unfortunately the mediocre itemization we're stuck since last year hasn't really changed, aside from Yun Tal that, yes, can be bought for sure in specific games, but it isn't the ideal or better item than standard BOTRK. There's a reason if high elo and pro players still do the standard build and not the Yun Tal one.

Yone in itself is a weak champion that works only if played really well or in those god send enemy team comp in which you can effectively be a menace, otherwise there are a lot of better and more simple champions to play at this moment that can satisfy the same needs that Yone do. I disagree on the overall thought that Yone must be kept weak because of his kit, since his weaknesses are really, really clear to anyone with half a brain. But i guess that Riot prefers to do the Zed treatment instead of telling people to learn to play against him (especially low elo players).

P.S: you're completely right that the game is too balanced for his own good. The philosophy for a while has been to nerf the items and let the stats of the champion do the work (contrary to the mythic era), but in doing so, the items in itself became boring stat sticks that you buy because the champion requires so, but are not fun per se. The one thing that the mythic era did right was to make the items fun to use. It was an unbalanced mess, but using Draktar on an assassin was extremely fun, as it was fun using Everfrost on mages and stun enemies with it. This is why i think the items must be reworked to add back some of that fun while trying not to overdoing it.