I don't think Tom saw himself as a "captive," but rather a wannabe brother to Michael and Sonny. Tom always chafed at Michael keeping him out of the loop, and there's a foreshadowing of the distance between them in the flashback scene at the end of II when Michael announces he's joined the Marines. Tom tells Michael that he and Vito went to a lot of trouble to keep him from being drafted, and how he and Vito had discussed Michael's future. Michael is furious and sneers," You discuss MY future with MY father?"