User blog comment:Astanas7/Fixing Skarner: Proposal 24§3c/@comment-1330314-20140215132416

The problem with perma-slows is that past a certain point they're impossible to counter: if your gets tanky enough or builds enough damage, their perma-slow won't allow their opponent to escape at all as they take them down. It also means there's no window of counterplay: a perma-slow means you will always get CCed if you engage you opponent regardless of how many abilities they've just thrown at you. It's much better design to have a really strong slow that lasts a limited amount of time than to have even a weak perma-slow.

I'd say give Skarner more time to see if he's really turned bad or not (his rework was only four days ago, for crying out loud), but if he really is weak than the duration or strength on his slow could always be increased to be more substantial.