The problem with the Renekton Bar is that it was a spectacular failure. Riot saw how Ren literally decided who did and did not go top lane, and wanted to buff all top laners up to that level. They then buffed four or five other top laners up to that level, and then had to stop because those guys were just steamrolling games because they were so powerful.
In the end, Riot learned that it was better to tone down one problem champ than to elevate many. Darius is very similar to Ren in that he's the best juggernaut around. In fact, he's a little too good at what he does and his weaknesses don't slow him down like they should. I wouldn't be surprised if the balance team already has a target painted on his back when they come back from vacation next year.
Some juggernauts aren't weak, but unpopular. Skarner is surprisingly strong, but no one plays him because the FDA has filed paperwork to have him labelled as a sleep aid. Yorick is much the same way, but instead of being incredibly boring he's incredibly frustrating instead. The AI on his ghouls and maiden artificially restrict his power since they often wander off and do stupid things when they should be doing something constructive. However, if those AI issues were to be fixed, Yorick would probably get nerfed because the biggest restraint he has is now gone.
Garen is legitimately weak because they indirectly removed power from him via nerfs to his favorite items over the past year. When he did get some compensation buffs earlier this month, they ended up giving him armor shred on his E. That fixed nothing because that wasn't what Garen lost from when he was balanced a year ago. He needs help getting to the backline to attack his villain, not more damage to kill things he shouldn't be attacking first as an anti-carry.
Morde isn't something you can fix with just higher numbers. They mangled his kit. Nothing short of a full VGU is going to save Morde from the trash heap. Although I will say the AI on Morde's ult is incredible. I've seen it change to better targets without me having to attack those targets first, ignore minions and go for enemy champions without being told, and actually zone off enemy champs when they try to enter it's general area. If Yorick's ghouls and maiden had that kind of AI, he'd be pick or ban by the end of next month.