You can always keep Chromium installed for the odd site that doesn’t work in Firefox (my daily driver). I do web development and test in every browser and I almost never encounter sites that don’t work in FF. The only one I can recall is something in the Azure Portal, probably because Microsoft wants you using Edge.

Typically, Safari is the laggard and any developer worth their salt would make sure their site works on iPad and iPhone. When a new web standard is released, usually Chromium supports it first but even then, not always. And web developers usually don’t use features that aren’t implemented across the board yet. I know I go to caniuse.com before I use something fresh out the oven.