I think it will bring Valve to dominating the console market in their class, a concept that you should be well familiar with, given your clear explanations of how like things should be compared.
Will it outsell the Ps5? Probably not on release, no. Will it be better than the Ps5? Probably, if only because it has broader flexibility.
Will the Steam Box outsell the Atari VCS, Evercade, and Polymega? Almost certainly, but hey, I'm only trying to compare like to like.
Will the Steam Frame outsell the Meta Quest 3 and the HTC XR and Vive Focus? It definitely has the potential to be super competitive if not on top.
Will the Steam Controller be the dominate PC-Console type controller? Maybe, the memory of the Old Steam controller is going to die hard and slowly.