I mean we are talking about trying to overthrow THE gaming giant. Smol MVP and expanding from there might be the right approach most of the time, but in this case you run the risk of becoming Epic 2, the store that took several years to add a shopping cart. And in that time where you’re expanding you’re in that awkward space where people would have to use both Steam and your system.
So I think it’s better to come out of the gate swinging. Obvs you should run lots and lots of internal tests, but as soon as you release to the public, you should be able to replace Steam for lots of people.
I could be wrong, but I rarely am :)