Website compatibility is inconsistent, extension compatibility is a slog, the desktop UI is confusing and nonstandard, WebKit itself is woefully incomplete, and on non-Apple platforms WebKit barely works covers conformance tests even with hardware acceleration disabled.

I don't use macOS anymore, but when I did I used Firefox without missing out on anything Safari would have given me. Now that I've abandoned macOS I don't think I can name one advantage of installing a WebKit browser on my system versus something Chromium-based.