Based on KP, Miller has the following record against top 25 teams:
2011: 0-2 (Clemson and Duke, lost by 10 and 46); finished the season 284 in KP.
2012: 0-3 (Georgetown, FSU, Duke, lost by 41, 15, and 27); finished the season 280 in KP.
2013: 0-0; finished the season 286 in KP
2014: 0-0; finished the season 315 in KP
2015: 0-1 (UNC, lost by 23 in Greensboro); finished the season 285 in KP
2016: 0-1 (UNC, lost by 33); finished the season 220 in KP
2017: 0-1 (UVA, lost by 25 in Greensboro); finished the season 121 in KP
2018: 0-1 (UVA, lost by 12); finished the season 82 in KP
2019: 0-2 (LSU and Kentucky, lost by 6 and 17); currently 82 in KP
Breaking this down, he's 0-11 against KP teams in the top 25. They were 0-2 at home against top 25 teams and 0-9 on the road. He lost five games in his first two seasons (first season I'm counting is when he took over as an interim coach). The odds of a team outside the top 200 in KP beating a top 25 team is single digit percentage for road, neutral, and for games against 10-15 teams at home (Wake is currently 176th and is 6% to beat 7th UNC at home, and 16% to beat 22nd FSU at home).
Just looking at these odds for the first six seasons when UNCG was outside the top 200, he went 0-7 with each game in single digit odds to win. His expected win total for these 7 games was under .5 of a game total. Overall, I'd say the expected win total for his 11 games against top 25 KP opponents rounds to 1 (so 1-10 overall would be "expected"). Winning zero when you're expected to be 1-10 means jack shit.
The real criticism, if you believe it is warranted, would be that UNCG still sat outside the top 200 in KP through five years. However, I believe the program was just in an abysmal state prior to Miller and truly took a long time to turn around (they ranked 99th in KP in 2008 and haven't had another top 100 team since 2002 until the last year and a half).