I said "is sorely needed" instead of "was sorely needed" for a reason. Despite Stoll's reputation for killing penalties, there isn't much that suggests that he will be a major upgrade for the Wild.
Stoll doesn't fare well when compared to Minnesota's PK unit, either. Here's a quick look at how every Wild penalty killer has done since the lockout season (out of 159 forwards with 200+ shorthanded minutes). Since the primary goal of a penalty kill is to not allow the other team's power play to score, I'm ranking them by how well they suppress shots.
As you can see, the Wild's fourth-liners (Carter, Porter, and Haula) are actually really good at penalty killing as it is. Even though Haula is struggling a bit this year, he still has outperformed Stoll in this regard. Stoll stepping in for any of them is likely going to be a downgrade. And if you (wisely) want to limit Koivu or Coyle's PK minutes, Minnesota actually has a decent grou of forwards (Granlund, Zucker, Fontaine) who've shown to be effective in that role. When you look at the options the Wild have at their disposal, it's hard to argue that Stoll will be a significant upgrade over what Minnesota already has in-house.
That's not to say that picking up Stoll was a terrible move- the Wild do need some depth at center, and acquiring Stoll required no risk. If it doesn't work out, the Wild can make an upgrade without any drawback, and potentially have him in an "In case of injury, break glass" box in Iowa. Still, this move isn't too inspiring given that (on paper, at least) he's underwhelming in the one area that's supposed to be his bread-and-butter.
*An asterisk denotes a player that has had 50+ shorthanded minutes, but fell short of the 200 minute mark. Their rank reflects where they would've ranked against the 159 players who did qualify.