Man, you hit the nail on the head. I'm 100% with you. Excellent post.
First off, Marion is an extremely gifted athlete who runs the floor great, rebounds better than any small forward, and produces nice offensive #'s. But you're right ... those strengths aren't what the Suns need at small forward with Marbury and Amare as the focus. Last year, as the 2nd option, he got a lot of shots, and his outside shooting was good enough to spread the defense to make the offense effective. This year, however, he hasn't gotten as many opportunites as the Suns have made Amare more of the 2nd option, and his shot has struggled. Perhaps bulking up had something to do with that. However, Marion's a scorer, not a shooter, and shooters don't need to be a primary focus of the offense to consistantly make shots from the outside. Scorers do.
Fortunately, I think Zarko is the right fit at small forward. He has the ingredients Marion doesn't have (good outside shot, ability to create and pass off the dribble, and good size), that should eventually complement Amare and Marbury. Unfortunately, when he gets healthy and plays more, it will take away from Marion's production, which could make him virtually untradeable because of his contract.
I'm not sure how to feel about the reality of the Suns management trading Marion. Obviously, it can't happen this year, as he is a BYC. Plus, big contracts on one position players are extremely difficult to trade. They gave him a huge contract not too long ago, which suggests he's part of their long term plan. However, Jerry and Brian are in love with Zarko and have been adamant about giving him more playing time, which suggests they feel his game is the right fit at small forward. Marion can't be moved to shooting guard, where his shooting and ball handling limitations would make him an absolute bust. So they're basically stuck with him and his max contract at small forward, the same position Zarko, the better fit, plays.
I've liked the suggestions of trading Marion for Ray Allen, who would be a great fit at shooting guard. I've always liked Steve Nash as well, but I'm probably alone on that one. These are just conceptual trades anyway at this point, as both Seattle and Dallas are set at small forward. But with a great shooting 2 guard and Zarko spreading the floor, complimenting Marburys penetration Amare's hopefully developed inside game, and this team could be unstoppable offensively.
They are going to have some tough, tough decisions to make next year.