K-State was the best B12 team at season's close. TCU won 12, went undefeated, lost the B12 championship in a nail-biter. They then beat the B10 champions, M. They obviously deserved to be there based on performance.
There are three or four elite teams, however: UGA, Bama, tOSU, and maybe some other SEC team, like UT every so often. Not TCU. The rest of us play hard but when it comes to nut-crunch time, we do not have the depth to compete with them. That should be obvious.
A 12-team CFP culls the TCUs of the world early in the playoff and elevates the elite like Bama. That's why moving to that format provides a better championship. TCU may have lost to Tulane in the opening round this year. K-State would have played the Vols in Knoxville and been dogs, not cats.