Ok, Shopify is then.

If you've ever used Woocommerce, the one thing you want to do is stop using Woocommerce.

A Shopify monopoly (and thus a shopify payments monopoly) would be very rough for a number of reasons

Indeed. I'm very grateful for Woocommerce, but since I use a tiny subset of its features, I'm "vibe coding" my own alternative with way less surface area and less bloat.