The Big 12 this year is one of the best conferences of the last 15 years so yea it's gonna fall back pretty hard. Especially when you lose players like Niang, Buddy, Ellis, etc. Even Tech loses Gotcher and Williams. The league will still be a top 5 conference nationally but as long as it isn't at historically high levels like this year then it's better for ISU.
I completely disagree with your notion that it's better to play in an weaker conference.