Johansson is really important to that power play for his zone entries. He's really good at skating the puck into the zone on the right side and then passing it back to Backstrom or Carlson.
Also I don't really think the Caps are playing bad at all. They had a disappointing effort against the Islanders, but honestly they didn't look terrible against the Panthers aside from Grubauer. I thought they played really well on the road against New Jersey and had the better of the even strength play against the Flyers. Admittedly the PP needs to get better but I think it is likely just from them missing Mojo and also just a slump. It happens, and like the poster above me said I'd rather it happen now so they can figure out how to execute a few more different set plays before teams figure them out in the playoffs.