"In the world of college football, that legitimizes the Cougars’ first three wins (against Pac-12 teams, two of which are not longer in the Top 25)"
Firstly, yes they are no longer in the top 25, because BYU beat them. Only 8 teams in the top 25 have a loss.
Secondly, they need to beat a G5 team to legitimize P5 victories? What world are we living in?