Originally Posted by Riolu
Mundo: Ignite isn't always ready and some mundo's can use their ults from a safe distance to keep their lane sustain. And we don't have enough items/skills that inflict grievous wound, nor many players to buy that 1 item to counter mundo.
Garen: His passive used right will net him some great sustain, especially considering how there have been a lot of ad casters trying to solo top and riot sucks at implementing AD spell vamp (you actually have to buy will of the ancients or hextech revolver for it)
Yi: AP Yi has become increasingly viable and now with this blow to AD sustain i wouldn't be surprised to see him jump in healing for 1k hp with 300 armor/mag res.
Ken really hit a lot of the points I would say to counter what you had to say.
If you're going against Mundo, there will be Ignites picked (note that I'm also talking mostly about "real" play. Not solo queue, blind pick, Normals), and a team is likely to be ready to counter a Mundo. Not to mention Tristana and Miss Fortune both have built-in grievous wounds so if a Mundo appears it's likely one of those two will appear as well.
Garen falls off hardcore and has to stand around for a good while to keep his passive up. In the event that Garen did become popular again, champs with at least one ranged poke skill (like Vorpal Blade or Parrrley) would be picked to counter easily. Or even maybe a metashift where there's more ranged charas top. Either way, Garen is probably never going to be seen in real competitive play for a long while.
AP Yi is irrelevant. You really need to rely on making sure you can nuke down at least one champ (gl with only one source of AP damage, esp if you only stack AP). It doesn't really matter how much his Meditation heals, he has to channel it and it's awful for sustain. And in a team fight, it's probably going to be over before he'll be able to even make use of his health.
Now, naturally a lot of different champs may cycle into the spotlight again with the Life Steal change, however it should be noted that just about anything works in Normal games if you have half a brain. Also, Wriggle's was given more Life Steal at one point in the recent past (I think it was when they changed it's proc, I don't remember) so it's probably going to drop it's pre-buff level, where it's still a good amount.