The narrative that somehow Safari’s release cycle is causing major problems in the "industry" or that somehow, macOS and iOS users are being left behind is false, especially for everyday users.
I use an old MacBook laptop running MacOS 10.7.5 with Safari 6.1.6, an ancient version of Safari by today's standards--about four years old--when I'm out and about. Otherwise, I'm using macOS Sierra with Safari 10.x on two different iMacs.
On the MacBook I use Facebook, Slack and many other websites without a problem. I get a warning banner on Gmail that says my version of Safari is no longer supported; other than a few cosmetic issues, I can send and receive email just fine.
The point: web developers have long figured out how to deal with multiple browsers across different platforms with different capabilities. Many differences and bugs have polyfills; it's not a show stopper.
Look, there are major features and minor ones; Safari has been at the leading edge with support for CSS Grids, wide-gamut color support, variable fonts, 100% of ES6, CSS Snap Points in addition to rendering speed and power efficiency.
There certainly have been calls to reduce the pace of new specs and releases so we developers can catch their breath and so that Apple, Google and Mozilla can release quality implementations--there's nothing wrong with that.