re: If Auburn finishes 7-6, would that make them mediocre?

SOS is a relative term and not really a good measure of how teams perform. For example, Team A plays seven games against opponents ranked in the 45-65 range for SOS and the rest of their games against teams in the 100-110 range. Team B only plays two teams in the 45-65 range and then ten games against teams in the 80-100 range. Without doing the math to calculate the stronger SOS of the two teams, which would have the higher SOS? Both would be fairly close but Team A played much tougher opponents while Team B only played two opponents that would be considered tough.

That's one fallacy of SOS. Another is pretty obvious. If you are ranked high and play a team ranked lower than you in SOS, then they receive way more benefit of playing you than you do them. You can't beat yourself.

Thirdly, for example, if Team B plays and beats a MAC team that ends up at 9-3 and Team A plays and beats an 8-4 PAC 12 team, Team B gets more credit for their SOS, even though most years an 8-4 Pac 12 team will be much better than a 9-3 MAC team.