Stable is the opposite of what I would call it.
Since Idaho and Montana were bounced in the 50's, the Pac-12 has not lost any members and plucked a school from a Big 12 that included Texas and Oklahoma.
A bad season on the field does not change the power dynamic.
If the Pac-12 wanted to pick apart the Big 12, they could. Everyone except delusional BYU fans accepts this (even the other Big 12 fans have confirmed as much).