I think they need to group up the champs like Nasus which are simply not fun to play against and figure out what to do with them. At least when I lose to a Riven or Wukong or Irelia top I feel like I got outplayed. When I lose to a Nasus/Yorick I just feel like there was nothing I could've done.
They actually do have a "short list" of champions who they've basically said will be nerfed into the ground the moment they start to see competitive play (Poppy most famously being the chair of the committee). The problem is that the goalposts are constantly moving, with new and better champion designs causing more and more old ones that were once acceptable to become "problem" champions as time goes on. Then you run into the problem of how to deal with it: do you try to just keep nerfing these champions until they aren't viable, but leave them as "training wheel" champion options (like Ryze)? Do you remake them, as they have with many of them? Do you change other parts of the game to punish the style of the play that makes them good?
There's a lot of moving parts there. I'd say Nasus has already fallen off pretty hard in professional play due to the Korean/Chinese meta being too fast and decisive for him to ever become a reasonable threat; it doesn't necessarily solve the problem with him in solo queue, where games tend to drag to a much greater length, but is having him be a bit of a pubstomp hero in exchange for being barely viable at the tournament level an acceptable trade-off?
There are similar problems dealing with champions like Fiddlesticks. Support Fid could be a real problem going into the next season, if they don't change the way support income works from their current test model: he levels Terrify early and has massive utility while he's getting his baseline "support" items, and then turns into a real problem late game once he can start building "real" items. You can't really lay a finger on him without making his already dubious jungle and mid-lane play completely atrocious, though. Do you accept he's a support now and balance him for that, do you try and get him back into the jungle or even mid, or do you just hope the changes you're making to assassins makes having him as a fear dispenser less attractive compared to AoE stun/knock-up supports?
Most of the "problem child" champions don't have easy answers, unfortunately. There probably needs to be a sweep of remakes on almost all the original launch champions who haven't gotten one to bring them up to speed with contemporary designs, but that's an enormous undertaking. The OGs are hard enough to fix that it's generally better just to try and remake the ones from the transitional period (like Yorick) who at least have a distant relation to the contemporary designs.