I think the analysis below may shed some light on our current conversation concerning the ACC versus the SEC. This is a pretty detailed summary covering the last 25 years. This shows each SEC team's record against all conferences including the ACC. This even goes so far as to cover every game during this period starting in 1998.
Without going into a lot of detail, the ACC has won 101 times out of 240 games against the SEC which is 42%. Not too bad. However, I believe the issue comes down to the ACC record against the SEC's top teams. The ACC teams do pretty well against the bottom half of the SEC teams, but the ACC doesn't do very well against the top 7 or 8 shown on the spreadsheet. Scroll down to see detail showing every team's record.
Complete list of the SEC's inter-conference football games since 1998 (the BCS and playoff eras).
topdan.com