ACC is not as strong as last yr.
This is categorically false. The ACC's Atlantic Division (the one Clemson plays in) was the 2nd most difficult division in all of college football this year, behind only the SEC West, according to the Sagarin ratings.
It has 6 teams ranked in the top 32 of the Sagarin ratings. The other, Syracuse, was in the top 40 before its starting QB Eric Dungey got hurt and Cuse got plastered in its late games (he missed the last four).
Clemson played a difficult crossover schedule. It played a road game at 17th ranked Virginia Tech, faced 15th ranked Miami in the championship game, and played 39th ranked Georgia Tech, as well. That adds up to 8 conference opponents who finished the year ranked in the top 39.
Last year's ACC had 8 in the top 40, as well, including Clemson. This year's ACC has 10 teams in the top 40 of the Sagarin ratings. The league is much deeper. Clemson also played its most difficult conference opponents away from home (Virginia Tech, Louisville, NC State, Miami).
Your belief that the ACC is not as strong this year is based upon your understanding of how good teams like Wake Forest and the like were this year.
Yes, Louisville struggled, but they went out of conference and CRUSHED Kentucky on the road. Virginia Tech got a neutral field win over West Virginia. Duke beat Northwestern. Virginia beat Boise State by 20 on the road. Louisville beat Purdue.
The ACC is every bit as good this year as it was last year, even if it's not as flashy (Louisville and Florida State being worse, while teams like Virginia Tech are better).