Losing to the only "strong" team on your schedule doesn't help you. You're better off being undefeated and untested, than already showing you're not good enough to beat the 5th-8th place team in the B1G.
While that's partially true, what your saying seems to forget, not account for, etc, that WSU has beaten 5th thru 8th place teams in Big 10, Big 12, in beating Wisconsin twice, UW 2 out of last 4 times that played them, and Texas Tech.
That's WSU beating 5 Quality P4 teams 5 times out of the last 9 times that played Quality P4 teams.
If WSU, OSU had remained the P2, WSU's rate of beating Quality P4 teams would have went down to 0,1,2 times out of 9,10 times.
If WSU had joined the MWC with BOTTOM feeders, WSU's rate of beating Quality P4 teams would have dropped down to 1,2 times out of 9,10.
When the PAC 6 becomes the PAC 8 of BSU, SDSU, Fresno St, CSU, Memphis Tulane, WSU, OSU, WSU's rate of beating Quality P4 teams like Winsconsin, UW, Texas Tech, etc, will probably be 3,4 times out of 9, 10 games.
It's not going to be 0 wins against Quality P4, like you seem to be saying, suggesting.