Yeah, the new Skarner is stupidly overpowered so it's kind of weird NNR calls it "just a slight buff" and "Shyvana and Elise are more OP". No, Skarner is (one of) the strongest SoloQ junglers in the entire game right now due to his massive strengths. Slow + Stun on a single ability alongside huge movement speed and attack speed buffs in at least two highly contested areas, a huge movement speed increase when he R's someone (and thus can drag that person WAY out of position) and with teams getting yellow support a lot more often now, he won't even need to make his own Righteous Glory.
If you think the buffs were "only slight", you're severely underestimating the changes to him. The Skarner Zones are a huge buff to him, as well as new items he can use properly.