Just looking at the players without considring positions, it's a definite win and I would make the deal.
However, because it's roto, you are essentially replacing Flash and McDonald with Ryan and Ladd, and St. Louis with Kessel, and you're giving up a goalie. Looking at it that way, it doesn't make quite as much sense. I don't think the gains you make with the skaters outweighs what you lose with Varlomov because it is easier to cycle goalies to make up games.
I wouldn't be worried about losing Varlamov and would move him for a solid offensive upgrade, but I dont' think you're getting enough of one here.
If you were to move Varlamov, who are some of the waiver wire goalies? You could add Ellis to give you the Carolina tandem, or Bernier for LA, which would make moving Varlamov more palatable.
12 Team H2H Yahoo Dynasty League
G, A, +/-, PIM, PPP, GWG, FOW, HITS -- W, GAA, SV%, SO
3C - Backstrom, Datsyuk, Stepan, Bozak, Ott
3LW - Neal, Hall, Ladd, E. Kane
3RW - Nash, St. Louis, Gagner, Callahan, Pominville
4D - Doughty, Phaneuf, Faulk, Campbell
2G - Bernier, Crawford, Dubnyk, Thomas
Farm - Karri Ramo, Ty Rattie, Joe Colborne, Brock Nelson, Joel Armia