I understand that side of it but valve goes above and beyond so much that even if Epic or Origin had huge user counts I seriously doubt they would put the effort in to building features like "remote play together" which streams a game to other people and streams their controllers back to you so you can all play the same local coop game. Or Proton which allows playing games on linux.

Valve even has linux kernel devs around who fix bugs in drivers for gaming hardware.

Steam may have been a monopoly but it was a pretty good one for the end user.