I never said anyone can compete with Steam in general, but Ubisoft offering a 20% discount on their own platform even if disguised with their own currency option is still a better deal for them than a sale on Steam.
AFAIK Steam takes a flat 30%, so Ubisoft has an interest in getting repeat customers to stick with their own platform. And every single person who owned a previous AC game has that launcher on their computer (and the 100 UbiToken to get the discount). So the entry barrier isn't really a problem in this case.
If I were to buy a game and had the option to pay 69.99€ on Steam or 55.99€ on another platform I also have an account on, I would buy the cheaper one.
The only point of my argument was that Steam players numbers should not be used as a metric for the PC sales and I think my argument WHY are reasonable enough to concede that there are likely a significant portion, if not the majority of PC sales, happening on UbiConnect.