Evasion itself has never been particularly powerful by itself- but it is banned because it is an oppressive mechanic that takes the focus of the game away from Rock-Paper-Shotgun by making moves like Vital Throw and Magic Leaf absolute necessary evils- and when the mons with those get sniped and stalling is setup, the effect reduces the ability to get back into the game (it's been a point of argument for a very long time, but the decision was simply that the evasion mechanic outright warps the focus of the game.) Before players often asked for "No DT/Mini"- games would outright end as early as the second or third mon down, because of a toxic stall that bought free turns on evasion in addition to the other stalling effects.
I don't think the caveat added last gen exists for real gamebreaking purposes- but as a matter of principle since banning evasion no longer outright bans certain mons. I don't necessarily agree with making rules based on principles of "making the game more skillful"- but the community made it's choice and when the discussion re-emerges, will make it's choice again. But the rule does have purpose in making the game far deeper than a parasitic mechanic like evasion allows it to be otherwise.
I don't really think people are gonna start running the BP 60 no-miss moves just because there are a few pokemon with evasion abilities out there; I know I certainly wont. But besides that point, we're trying to have a civil discussion as to whether or not an occasional miss against a select few pokemon under their respective weather is broken/unbalanced/uncompetitive/etc. And so we don't get caught up in opinions which could be thrown out all day, I'll lay down some facts:
- Every person who has a soul hates minimize/DT. I tried to defend evasion earlier at one point, I was a fool back then.
- The ability "Serene Grace" literally doubles hax. Not banned because it still takes an amount of skill to use
- The ability "Super Luck" (Doubles crit chance) not banned because it really doesn't make that much of a difference in the metagame
- Confusion mechanic not banned though based ENTIRELY on luck (smh at mass popularity of that motherfucking set-of-keys pokemon)
- Evasion abilities up evasion by 20%, so the equivalent of the accuracy difference between hydro-pump and surf
- Chance of that Magic Guard Alakazam using Life Orb vs. Focus Sash: 50%. Chance of my Garchomp's dual chop missing (because I want to break the possible sash): 10%
Look, if you haven't got it already, my point is that luck is an integral part of the game whether you like it or not, and there is a lot of it. And in my opinion, banning 2 niche abilities because something doesn't always go your way when you're against them, well that just seems childish to me (especially after the nerf this gen).
edit: And yes I know the point of banning this in the 1st place was to try to remove the luck factor as much as possible, but this isn't a meta-game changing mechanic. It's more of an occasional "get out of jail free" card ability. And this is besides the point, but you gotta admit it's a lot less OP than Magic Bounce, or any of the weather starting abilities in 5th gen for that matter