You can be a great team running a pass happy air raid, but your margins are thin if you can't run and the other team gets a few stops. You can win with a power running game, but the margins can be thin if the other team puts 8 in the box and plays man and you don't have a guy who can hurt them for doing that. Having a strong running game certainly helps the passing game making play action more effective and enticing safeties to play closer to the line. But a strong vertical threat, especially a speed guy who if he can beat a jam at the line can blow up man coverage loosens things up for the running game too.
I get the emphasis on big bodied receivers that can win jump balls for the deep stuff and are effective as possession receivers and great blockers, but having a viable speed merchant out there really changes the dynamics for the defense. If we go with two big WR's who can do the jump ball, possession and blocking along with a TE that still leaves room for 1 faster WR. That seems like an ideal lineup unless we go 2 TE, 1 big WR and one speed guy. Love me some 2 TE lineups as long are both at least competent as both blockers and receivers.