He was what, 8th overall in scoring? I'd say there's less than 7 teams.
Very few teams would take guys like Kessel over E. Staal and Ryan Getzlaf to name but two forwards who he outscored. There's many teams where he wouldn't be the best forward:
Anaheim: Getzlaf
Boston: Bergeron
Buffalo: Vanek
Calgary: Cammalleri
Carolina: E. Staal
Chicago: Kane/Toews
Colorado: Duchene
Columbus: Prospal
Dallas: Benn
Detroit: Datsyuk/Zetterberg
Edmonton: Hall
Florida: Huberdeau
Los Angeles: Kopitar
Minnesota: Parise
Montreal: Pacioretty
Nashville: Legwand
New Jersey: Elias
New York Islanders: Tavares
New York Rangers: Gaborik
Ottawa: Spezza
Philadelphia: Giroux
Phoenix: Vrbata
Pittsburgh: Crosby/Malkin
San Jose: Thornton/Marleau
St. Louis: Stewart/Backes
Tampa Bay: Stamkos/St. Louis
Toronto: Kessel
Vancouver: D. Sedin/H. Sedin
Washington: Ovechkin
Winnipeg: Kane/Ladd/Wheeler
Kessel would
definitively be the best forward on Calgary, Colorado, Columbus, Dallas, Florida, Montreal, Nashville, New Jersey, Phoenix, St. Louis, and Winnipeg. That's 11/30 teams.
You can make an argument that he would be the best forward on Boston, Buffalo, Edmonton, Minnesota, the Rangers, and possibly Toronto (Lupul is arguably as effective when healthy) and San Jose (due primarily to age). That's another seven teams out of thirty. That's 18/30 teams.
It's hard to say that he would be the best forward on the twelve remaining teams (listed in bold).