I don't think that mucking it up and then laughing as guys push him around is the kind of "fight" that the team really needs. It's something, but the team needs smart, simple, and physical play on the forecheck that eventually goes to the net for ugly chances. Krebs doesn't do any of that.
Krebs gets all kinds of slack for "playing with slugs". Most of which were Girgs and Okposo who aren't actually slugs, and were outproducing Krebs for the first couple months of the season. Mittelstadt played with slugs last year in Asplund and Olofsson, and he still produced and earned his time higher in the line-up. Krebs has been given a 3C role simply because the front office decided they wouldn't pay the better player. The only slack Krebs deserves is that he still has a year or so to develop into a better player. As of yet, he's shown little to expect much more, regardless of linemates.