There is nothing wrong with the tie-breakers. If using head-to-head the way you want with SMU-Miami-Pitt-GT-Duke all having two losses: Miami would be eliminated, Pitt, would be eliminated, GT would be eliminated, and Duke would be eliminated. IF SMU had lost to Duke, the SMU would be eliminated also. You can't take the head to head of two teams in a multi-team tie and start promoting or elininating teams based on it, unless they are all common opponents. You could argue about using something else as the next tie-breaker, but the strength of your schedule is a good one.
The big issue is that there is not a definitive way of breaking the multi-team ties. You have to pick something, and stick with that no matter how it affects your speficic team that year.
A larger issue for the conference is that with the OOC wins/losses and strength having no impact on ACCCG tie-breakers, it sets up a case where a team that hasn't won any OOC FBS games could go to the championship game and cause the conference to have zero teams in the playoffs. They should look at having rules about being at least .500 in OOC games to make it to the ACCCG. Maybe only allowed 1 OOC loss to make the game. I wouldn't really like that, especially with GT having 3 P4 OOC games next year, but something needs to be done to keep the ACC Champion from being a five loss team.