Sure, on defense. But the stronger more physical forward always has a bigger role on the boards, on defense, as well as offense. On offense, the SF (Griffin) is primarily a perimeter player while the stronger forward more often sets up low, or at the high post. Always has been true. Some years the two forwards can be inter-changeable, but this year, Guerrier is the only forward capable of strong inside play. You need at least one of the forwards to contribute with toughness on the boards. Marek isn't going to provide that.
If you want to be mediocre, take Griffin or Guerrier out to give developmental minutes to a bench forward. If you want to be more lame on the boards, let Guerrier sit for a stretch.
Now, if you want to talk SG, top of the zone -- different story. I believe Griffin could play the role.