I think there are enough eyeball tests for the Big 12 to pass as a P5 rather than a G5, although to be clear they're certainly at the line. Let's say media rights don't pan out, I still think this group of members can pull more than any other G5 conference. I would expect most members of the conference, excluding Kansas, to probably beat most G5 conference games they play in. Most importantly, they have a member who has a consensus national championship within my life time now with BYU. Every other P5 conference has multiple, but the G5 conferences all have none. The Iowa State dude above who has been melting down also notes how the new Big 12 would have two top 10 teams in the AP rankings right now, which no G5 conference has ever done.
Like, for all the shit the Big 12 got, it never was a bad football conference in terms of performance. Many seasons, it was top 2 in terms of competitiveness. I think the Pac 12 is overall a worse football conference outside of the heavy weight. I just don't feel like if you take out the top teams in the Big 12, the rest are instantly worse than all the other G5 conferences. Like, perception is king, and I still think schools like Texas Tech are historically a step above, say, Tulane.
I think the Big 12 has juuuust enough residual clout among all its members, plus juuuuust enough accomplishment in my lifetime, to differentiate themselves from G5, especially once playoffs expand.