for example have been gutted more than once into unviability because they were "oppressive"
Meanwhile 
exist when they have the most overloaded kits with multiple passives and extra stats.
It's ridiculous how hard Rito has tried to make melee carries a thing at the expense of the enemy team's fun.
"Gutting" a champion is a stupid way to try to balance something, that's what happened. If the champions you were trying to balance end up needing buffs when you're done, you have failed at balancing them.
Literally all of them got nerfed and will receive further nerfs. Both directly and probably indirectly with the ADC rework.
"Oh but Yasuo didn't get any nerfs in a while and probably won't receive more" Correct because Yasuo has one of the most expensive builds in the game and 90% of his laning phase is dependent on lv 1-2 cheese.
"But I always die to him when he does that!" Yes, yes you do.
Being oppressive is okay as long as you're not
Yeah, Lulu mid/top is still allowed for 2 damn seasons.
Why isn't that shit gutted yet?
/s
Cassio was oppressive? When?
Honestly, though, I'd say she is now more than before this whole rework thing. Level 2? QEEEEEEEEEEEEEEEEEEEEE. That's cheesier than lane Nunu.
PS. Yasuo was nerfed like 10 times in a row. Completely untouched.
Darius doesn't have a remotely overloaded kit, just an overtuned one. He's entirely immobile, strictly melee, and has unremarkable CC. His strength is entirely numeric in nature, and that's probably not even an issue after the latest changes to him (remember that Worlds is on an outdated patch). I'd say that Mordekaiser is in a similar boat, with zero CC, almost no mobility, and very time-limited windows of range.
Here's the thing. The champions you say got gutted had that happen because there was not a numerical value at which they could work. The problems ran deeper than numbers changes alone could fix. Of the champions you list, I don't think that's the case with any of them. Fiora has really interesting and skill and counterplay intensive patterns. If they're too strong right now, if she's just able to right click on people and annihilate them, drop some numbers and force her to use her passive. A similar approach seems to be working for GP, though in his case, a steep skill-curve could make him hard to balance for the experts and the novices. Yasuo and Riven do have issues of depending more on the player's strength than on that of their opponents, but Riot's working on changes to Riven.
I can see cases, like old Eve and current Poppy, where the appropriate thing to do is to make sure that a champion is too weak to see competitive play, because the alternative is worse and there isn't the bandwidth to do an immediate rework. But that's a last resort, for when simple numbers tweaks or small functional changes aren't enough to get the champion back in line. The same complaints you're making have been leveled not so long ago against champs like Zed, Thresh, Vayne, and Lee Sin. Champions who, I note, are currently pretty balanced in competitive and solo queue and who have not received reworks, only numbers changes.
Basically, be sure you know that number tweaks won't be enough. I think in the case of nearly all champs you listed, they will be.
Not trolling but is Riven even still a thing? Most of your other examples would wreck her.
You know how many games I've seen in since his rework? 10 or so. Maybe 15, if I'm being generous.
You know how many I've seen him in since the last nerf? 0.
The guy has been perma-banned to death in yolo ques (which is very different from pro play). This means that it's really, really, really difficult for Riot to get a pulse on where he is. Whether he's actually too strong and or why he might be. Quite frankly he's probably fine since his last nerf, but people still won't leave him unbanned. Personally I wish he hadn't been touched at all.
That said.. Are you really calling overloaded? That's a joke, right? He doesn't fit the criteria you yourself even stated. He doesn't have a ton of free passives laying around, he doesn't have boatloads of extra stats unless you meet certain criteria, ect. Just taking the popular champions to hate / champs you don't like and calling them "overloaded and free stat machines" doesn't make it true. 
is pretty much the definition of a "free stat" champion. He gets huge amounts of AD from his Q, reduces enemy AD, gets gigantic amounts of movement speed, attack speed, and % healing received increase from his W.. And gets a gigantic amount of free health, armor, and MR from his ulti (which scales with that % healing from his W). He's got more free stats in his kit then any of the champions you listed, yet I don't see anyone bitching about him.
It's fine if you don't like a champion, but please be intelligent in your discussion. Just throwing out the cool and edgy buzz-kill words doesn't make your argument more valid.
What if instead of nerfing these oppressive champions Riot just simply buffs all the other champs. Just remember when everybody's over powered no one will be. At least that seems to be dota 2's idea of how things should.
You are forgetting 
being gutted into oblivion.
Everyone forgets T^T
