USC had beaten up on mostly cupcakes (except for Arizona), and with the leading candidate for the Heisman being front and center, of course the media was going to hype them up.
They were a good team, but the combination of a horrible defense, along with Lady Luck being ever so fickle, basically deflated what was a promising start. Keep in mind, they had a legitimate chance of knocking off Washington, Utah, and Oregon, but came up a bit short.
Had they won those three games, then I think it could have been one of Marcus Freeman's signature wins, but beating out a team that finished 8-5 isn't going to be worthy of being called as such.
I could see someone calling the 2022 Clemson win a signature win for Marcus Freeman, but that's being generous, since Clemson finished #12 that year.
The last time we had a indisputable signature win was 2020 against #1 Clemson, since they were also a playoff team and finished #3. Even then, we weren't facing Clemson at their full strength, since the bulk of their front seven (all of whom were NFL draft picks, if I recall correctly) were out due to COVID. When they came back in the ACC Championship game, they took us to the woodshed, and we essentially became their signature win that year...