On the one hand - yes, your argument makes sense.
On the other hand - B10 and SEC teams getting beaten earlier in the playoffs may expose them as being overvalued and could lead to additional B12 spots in future playoffs - which would also benefit BYU.
I guess you just have to say that you have a different opinion as to what benefits BYU the most. But I don't think you can quantify it and say that BSU beating Penn St objectively has a more significant impact on BYU's football future and BYU's future in the playoffs versus having most of the B10 and SEC teams get knocked out in their first game. I could accept arguments for both perspectives. And until it happens - we won't know which is right.