If it's about blind TV markets...ala "rutgers brings New York"...then the new Big 12 has way more population than Pac 12. (huge chunk of midwest, Texas, Ohio, Florida, Utah, WVU)
If it's about who has the actual most fans that will actually watch tv, actually stream, actually buy streaming services just for football, actually buy tickets...the remaining 8 or the new Big 12 have more of an advantage too.
By either metric the Pac doesn't have an advantage. I think some of the ACC markets are pretty weak in the "actual fans" metric as well, although obviously the ACC footprint has massive cable tv population footprint.