The emergence of Clemson as a national power definitely helps the prestige of the ACC, but it remains to be seen if that lasts once Watson leaves for the NFL (see Oregon and Miami). At the end of the day the ACC still only has one blue blood football program in FSU. If FSU leaves the conference is done.
The Big Ten on the other hand has four blue bloods (PSU, OSU, UM, NEB) and a bunch of other top end programs (Wisconsin, Iowa, Michigan State)
Did the ACC have a good year in 2016? Sure, but at the end of the day the Big Ten and SEC will always be on the top of the CFB food chain.
The Pinstripe Bowl is a great example. Pitt was arguably the third best team in the ACC this season and couldn't get past a 6-6 Northwestern team (although we were better than our record indicated). Imagine if you played Wisconsin, Iowa, or Minnesota.