I still don't mind this trade. The C's "window" closed when Ray was kneed by Artest. The 2010/2011 teams had more holes in than swiss cheese: no post offense, poor spacing, offensive droughts, turnovers. All the same holes the C's covered up in years prior were more pronounced because the core of that team was older and banged up and they had no depth.
This trade was meant to give them depth, but Green didn't catch on and that aspect sucked. OTOH, I am hard pressed to see how this would have been better with Perkins. Perkins wouldn't have helped them break their stagnant offense, he also wouldn't have eased the burden on Pierce or Ray who had to chase better younger players around the court. He would not have made Garnett 5 years younger.
So arguing about last year is moot. Sure they were the best team in the league early on, but their age rendered them ineffective in May and June.
What this trade did was gave them financial flexibility moving forward and healthy players last year. If you want to argue it robbed them of a championship opportunity, then that's your prerogative. Personally, I don't think they had a snowball's chance with Perkins or with Green considering the state of affairs with the rest of the team.