As much as I've disliked Glen's game and how overrated he is on the board, and factoring in that I genuinely don't want to see him play anymore, I would have to say that he is not THE problem like you've said. To me, here are the problems in order:
1) Team chemistry (goals aligned, etc)
2) Health of KG, Pierce, etc.
3) Declining stars
4) Lousy bench w/o Daniels. This is where I put in Davis. He's subpar and I don't think he should be getting more than 5 minutes a game on a championship caliber team. Nonetheless, he's not #4 on my ranking, the whole bench is.
5) Sheed not playing up to his potential.