That's all well and good, but has nothing to do with Adam and his schedule. During the pertinent time period, he was in Los Angeles two days, and was performing a concert both nights after doing a concert in Vegas the night before his arrival. His material is vocally demanding, and for those three concerts he sang for 90 minutes straight,except for brief breaks for costume changes. Add in sound checks, and that's a lot of singing. He had to leave for Toronto the next day. How is it reasonable to expect him to also rehearse and tape a performance for Idol - even if by chance the schedules for the others in his theoretical group performance had allowed it, which is a big "if"?
Jennifer Hudson was not able to appear on Idol at any other time during the season. Through careful scheduling, Adam was. If there were fans who were not satisfied with the solo showcase he was given by the show, at the only time he was available, that's really not his fault.