So your argument is that Thabeet is was and always will be a stiff? At the NBA level maybe, but he was a dominant big in college and not close to a stiff by his junior year. I'm not even sure stiff is the appropriate word for Thabeet at the NBA level. He is fairly athletic and mobile for his size, he's also not the greatest basketball player ever and has had some mental issues. He started as a very raw freshman and developed immensely because of JC and Blaney, but even they couldn't make up for 15 years of not playing the game. He is, was and always will be raw relative to other NBA players, a stiff conjurs someone far less athletic to my mind.
As for Chukwu, who knows where he will/would develop better. Thabeet should be his floor if he is developed properly, a more agile Hibbert his ceiling. Do you think PC gets him to his floor/ceiling, above/below if he goes there?
Drummond didnt devolop a ton at UConn but he did get better. His game was always more suited for the NBA though.