Literally every reworked champion hit the ban list instantaneously because t hey're massively overtuned, I don't think the reworks failed overall, I said they failed in terms of balance.
Darius actually isn't underwhelming, he takes a little practice and goes full insanity. His initial launch made him a touch weak, but a hotfix of damage on his Q and a buff to the heal of missing HP, made him crazy strong.
Skarner is so overwhelmingly dominant in the jungle he saw a 65% win rate upon release, and even after hot fixes he remains around the 65% win rate mark.
GP and Fiora become overwhelming after their first items, and even before if they're played at a very high level. I love his kit, he's so much fun to play, but as soon as he gets his first item he can be completely unstoppable from that point on if played properly. Fiora just goes ham with that true damage after a small window of weakness in the early game against lane bullies.
I overall like the Garen rework, so I probably shouldn't have included that as a "failed" rework, I think he's probably pretty balanced for the most part.
Finally Mordekaiser is very lane dominant with the proper support, frequently kills in lane without jungle assistance, his Q can 1shot on it's own, and having dragon's ghost cheese the crap out of lanes and take towers is nuts. I personally like making it gank bot lane through their tri brush, it's hilarious to see the reactions when a dragon comes out of their tribrush instead of a jungler. His damage numbers are way too high, he's basically a free win in most cases as long as the team plays around him properly.
Almost all of the champions above win lane, unless against one another, their numbers are a bit over the top in how they play out, and will likely take several more patches to even attempt to balance.