I suspect having McClellan in charge was good for the CSA as to Lee's motives I couldn't say but I think Lee liked McClellan from what I've read he certainly didn't dislike him.@Scott1967 posted somewhere above that Lee was disappointed when McClellan was removed from command and that he rated him as his most dangerous opponent. There might have been an ironic undertone to it, but I would also guess that Lee might have actually meant it when he said that. McClellan certainly didn't make things easy for him - case in point, Lee's casualties when going against McClellan.
I've learnt a lot on this thread some of the postings have been first class I thought I knew George McClellan turns out I didn't know him well enough , You cant call him a bad general anymore his first major battle and a draw with Bobby Lee that's not too bad considering what came after.
https://civilwartalk.com/members/saphroneth.19683/ and https://civilwartalk.com/members/67th-tigers.636/ have given me and education on the quality's of McClellan and in a way I've change my opinion on him well you live and learn in a way.