The move to the ACC is a rough turning point in the program, but it's correlation, not causation. Syracuse had a helluva first year in the ACC. Sanctions combined with a failure to address Boeheim's retirement at that time is the biggest issue.
The sanctions themselves are a separate issue (not debating the justification of those sanctions or their overall effects), but a competent AD would have closed the book on the JAB era through a phased retirement and enforced the transition to Hop. JAB's ego and stubborness convinced him that he was the only one who could shepherd the program through sanctions and then Buddy was developing into a high D1 player, which colored the rest of his roster management leading us to where we are now with a poor roster, limited defensive and offensive capabilities and no real future.