Most championship caliber teams have one game like that every year. Syracuse and Dino Babers play Clemson tough. Beat them in 2017. Gave them fits in 2018. Pitt has also had Clemson's number in years passed.
No, beating Clemson isn't impossible—but the Clemson you get in an ACC Championship game with the Playoffs on the the line (something they've made every year since that system was implemented years back) is a far cry from catching them on a Saturday afternoon late September; a day when Trevor Lawrence was also knocked out of the game in the first half and Travis Etienne played the duration—rallying them from down 16-7 at the half for the 27-23 win over the Orange.
Your rationale is in line with 2001 era Nebraska fans saying Miami was beatable because the Canes needed a miracle play late in the game to survive at Boston College—only up 12-7 in the final minute with the Eagles looking like they were about to punch in a game-winning score, or that Virginia Tech had the Canes down to the wire and was a two-point conversion from sending that regular season finale to overtime in Blacksburg.
Neither game was indicative of who UM was as a team in 2001, anymore than a close call against Syracuse defined a Clemson team last September with a third-string quarterback rallying them to victory.
Miami needs to be more concerned about a September 7th road game at North Carolina—and holding home court against Virginia Tech, Virginia and Georgia Tech before back-to-back road game at Pittsburgh and Florida State—than they do anything else right now.
Canes are 1-of-15 in regards to winning the Coastal; hence the statement that just getting to the ACC Championship game Manny's first season would be a **** of an inaugural year. Get that far with 12 games in the books and then we can worry about how beatable Clemson might be come early December.