Caron Butler has an eFG% of 41%, 42% and 43% on his jump shots for the last three years.
But he also has 28 double doubles and 3 triple doubles, he's a more complete player (at this point in their respective careers, Caron's got nothing on a Prime Ray Allen). Plus his percentages will skyrocket from being on the floor with Pierce, Garnett, and Sheed.
I don't know about that. Caron Butler has struggled offensively this season because he has been surrounded with more scoring threats. Just like he struggled in Miami once Wade + Odom arrived and how he struggled in LA with Kobe + Odom. When he's asked to play alongside other threats, his offense drops.
Caron Butler's most efficient offensive seasons have come when Arenas was injured and he was allowed to be the main offensive threat on the floor. The ball always came to him and he had the freedom to do whatever he wanted with it.
Maybe his offensive efficiency does improve when Butler arrives in Boston ... but throughout the rest of his career it's gone the other way and I think it's more likely that that pattern continues than not.