In many respects Apple is not keeping up with Chrome and Firefox in terms of new features.
In particularly Apple is not supporting or poorly supporting features associated with "Progressive Web Applications" on mobile to prevent PWA's from competing with the app store on iOS.
Apple is in between a rock and a hard place on this. Webkit activity really slowed down a lot. Apple is pretty much the main contributor. It also gives them the most flexibility to incorporate into their products. Blink engine is very slow on the Mac/Apple products, and would put Apple at the mercy of Google ultimately. The Gecko engine is something they could probably use, but there are a lot of "mixed" opinions on how good the engine is.
Sidenote:
I love Apple products, but to be honest Apple is not the best at making software. Recently, the quality has declined too. Their great applications are a few niche professional apps not designed for the average user. They have also gotten a lot slower at releasing updates.
Dunno... I do a lot of web browsing on an iPad and don't notice a problem with it.
I am a software dev at work and we had a time period where our product (React-based SPA) wasn't working on mobile Safari because of 3rd party cookie issues -- in the long term though the world was going that way and once we changed our cookies Safari works just fine.
In particularly Apple is not supporting or poorly supporting features associated with "Progressive Web Applications" on mobile to prevent PWA's from competing with the app store on iOS.