IMHO this supports the original point that payment via Steam would be an upgrade:

Sending cash to a postal address isn't low-effort nor low-risk.

Payment by cheque is something I have never done, nor would I know how to do it. I'd have to ask at my bank -- not low effort. I don't know if I'm an outlier here but I have never heard from any of my peers who ever did such a thing.

The same or even worse is true for international money orders. The whole concept of making a money transfer to a postal address is something I have never heard of. Where's the IBAN?

The Wine team is right to put even PayPal before all of these.

Yes, I do. It just means that you have to manually "recharge" your Steam wallet when it runs low. That's some effort, but it limits the possible damage if something goes wrong.