If you want website to not be broken on Safari, the solution is to give developer without a Mac the ability to test on Safari. I wouldn't be able to fix my site if it's broken on Mac Safari if I don't have a Mac.
I support an Open web, I test my websites on Firefox and Chrome, I even occasionally do Edge testing, and I develop my websites often primarily in Firefox. But I'm not buying an iPhone or a laptop just to test websites, so I don't test in Safari.
Every other browser has a way to emulate in Linux, I can even download free VMs from Microsoft to test IE11 in Windows (and Edge now runs in Linux). If Apple isn't willing to make its operating system available to me to test on then I don't see why I should feel obligated to test on it.
And given that there is some Mac-specific behavior for Safari/Firefox that I've run into (differences in how blur works), and I generally can't assume that all of my stuff is going to work perfectly, I'm either going to fall back on progressive enhancement or (in the case of a complicated webapp) I'm going to tell users that Safari is unsupported and they're continuing at their own risk.
I'd love to support Safari. All Apple has to do is give me a way to.
Unfortunately that's not enough, for two reasons:
1. Safari is the only browser that is still tied to OS release versions, the WebKit version used by Epiphany is rarely the same, so results will likely differ
2. Epiphany has no mobile emulation mode. (E.g., I had to work around around an annoying input zoom bug in Safari/iOS by blindly applying the least stupid solution I found searching the net)
However in the IE era, even though Netscape/Firefox was free for everyone to test on, many large companies made their sites for "IE Only" because it's easier and cheaper. What I worry about is that, even if Safari kept up with web standards and was mostly compatible in terms of the basics, sites would start requiring APIs that only Chrome wants to support (e.g. FLoC). This would give Google a lot of leverage to push its own technologies on users (Amp also comes to mind).