Where they 'should' be doesn't really matter.....
Typically you should fall more than that when getting beat by the #15 team. I think they should have fell at least under Georgia and probably under Ohio State in the AP Poll.
None of it is fair. 'Best' is relative. MSU is better than some Top 25 teams, but in our current system, better records get you ranked. Until more cross pollination is done with our OOC schedules, this will continue to be the case. MSU's schedule is easy by the pundits' measure, but it had us ranked #11 at one point. That's just the system will all abide by. Did anyone really think Louisville was a Top Ten team? Of course not, but plummeting in the polls is the price you pay when you lose, just as being ranked is the award when you win.