Half of the Big12 teams have been in the Big12 for one season or less. Teams don't magically become more physical just by becoming Big12 members. BYU, Houston, UCF, and Cincinnati are still building P4 depth. Colorado is still Colorado, ASU is still ASU, Zona is still Zona.

A few teams will be more physical than the average Pac team. Kansas State is a traditionally physical team that had a good run defense last year, and Iowa State's defense was pretty good last year as well. Defensively, Oklahoma State was not good, neither was TCU or Baylor. Kansas, Texas Tech, and WV were all mediocre defensively.

I know physicality is more than just defense, but we know Utah's D can match any offense when it comes to physicality so I won't bother.

This isn't the traditional Big12. This is the Big12 minus the two best teams in the Big12, with the addition of a bunch of non-Big12 teams. The Big12's former reputation for being physical (if the Big12 ever had such a reputation) does not apply to the current Big12.

TL;DR: there are a few teams that will present a challenge in the physicality department. The rest will not.