They probably will drop a spot.
However championship wins and losses do not count the same as regular season (unless the loss is a blowout).
Everyone is playing an “extra” game usually vs a quality opponent; while everyone else is not playing.
A championship win is thought of as more than a normal win. A championship loss (non blowout) is thought of as less than a regular loss.
It’s been that way and Really why shouldn’t it be that way?
In TCU’s case, in a weak conference it could look bad. How can you not won that weak conference and expect to win a playoff?