Why is it a better conference for Syracuse? Is it because you have nostalgia for the conference of the 80s and 90s? Does playing Xavier, Creighton, and Marquette actually make more sense than playing Clemson, Wake and Miami? Does playing Georgetown, UConn, and St. John's actually help recruiting more than playing Duke, UNC and Virginia in 2023? I mean sure, its fun to pretend like Nova and Georgetown games carry the juice they did in the late 80s but if JT isn't on the sidelines does it really carry that much old school excitement? I don't think so. Did anyone actually care about the saint john's games the last decade Syracuse was in the BE? It was just another game on the schedule. It held more significance to me because I grew up watching those teams, the kids today probably have the same feelings about ACC teams because those are the teams they are watching.
As for the ACC decline I think it really is pure coincidence that Syracuse's decline occurred at the same time as joining the ACC. Sanctions + Hopkins leaving + the rise in southern programs (via prep schools) + JB losing his edge is what caused the downturn. The conference affiliation really had nothing to do with it.