More than... 3 champs per role...? Idk if you and I watched the same tournament or not, but I just looked up the stat to be sure as well; there were 45 different champions played at MSI 2016. That's, on average, NINE CHAMPIONS PER ROLE. Whether that stat were as high as it is or not, it wouldn't matter anyways; comparing professional play to regular play is kind of silly. They have completely different metas from us usually both in champ select and playstyle and Riot has been pretty forward saying they refrain from balancing based on pro play as much as possible.
As for only giving light buffs/nerfs per patch to outlier OPs and stuff, that's because they don't want to under-break the champion, either, and these seemingly small nerfs or buffs can have really significant impacts on a game, especially on champs like Zed who are all about early aggression and snow-balling. If he can't be aggressive early, he falls behind and is essentially completely useless. In his current state, however, it's the opposite. He's too strong and therefore snowballs too hard, being able to one-shot even tanks given he builds and plays right. Finding a balance of him being able to snowball a lead for his team (while not snowballing too hard) and also not just being useless early and therefore useless late is much more finicky than it seems. There's such an absurd amount of math that goes into everything and there are so many item combinations and such as well, that it's incredibly difficult to properly balance a champion without breaking it in one direction or the other. Look at what happened to Fizz! He was too reliably one-shotting everyone with his basic combo that they had to move more power onto his ult and away from his other abilities. What they DIDN'T take into account was that people would then try building AD on him instead, which, with the increased damage from his ult, was EVEN MORE RIDICULOUSLY POWERFUL.
Basically, all I'm saying is, balancing is a trial-and-error process and it takes time. People are working on the things we want them to be working on, but there are priority lists and different teams and a lot more work than I believe people think there is going into everything over at Riot. It's not as easy as just flip-floppin' some numbers and calling it a day. For instance, just above, you called a light attack speed nerf meaningless, but a light AS nerf at early levels means it's harder to clear waves as someone with relatively limited aoe damage, which means it's easier to aggress the person early when they don't have enough levels to fight yet and then they lose minions under tower, so they don't get as much farm, so they don't get their item that they need as quickly, so they can't get a kill to snowball off of, so they can't carry the game the way they normally would be able to. Obviously, I'm using a bit of hyperbole here, but my point is that snowballing works both ways, so a lot of care has to go in to making these kinds of changes.
