There has been a bunch of mediocrity in the ACC besides Clemson, but I'm not sure I'd say all teams are equal in this regard. Here are the ACC records since 2014 (using same timeframe as above, going back 5 years to the last season Duke was above .500 plus five seasons seems like a reasonable timeframe):
Code:
team win loss Pct
clemson 44 4 0.917
FSU 29 19 0.604
pitt 28 20 0.583
miami 28 20 0.583
va tech 27 21 0.563
lville 26 22 0.542
unc 23 25 0.479
gatech 22 26 0.458
nc st 21 27 0.438
uva 20 28 0.417
duke 19 29 0.396
bc 18 30 0.375
wfu 16 32 0.333
cuse 15 33 0.313
I would argue that (in addition to Clemson) FSU, Pitt, Miami, Va Tech, and Louisville have been mostly "above the middle" and are in a different tier for this timeframe than the rest of the ACC teams.