Blink was forked 12 years ago, and the size of the team behind Chrome is probably at least ten times the size of the team behind Safari. So yes, there are major differences between two, and it's not just additional advanced APIs like Web Bluetooth. WebKit is lagging behind in all areas and ridden with bugs.

I doubt it's "at least 10 times the size" and probably somewhere closer to 5X tops with a 2X core that's the realistic measure since those are the non-rotating folks with real expertise who make things go. That team is probably about the same size as Mozilla's which is also non-rotating.

There are enough weird divergences to make targeting iOS annoying. Off the top of my head I can recall that Safari PWAs can't get callbacks from pages spawned in a new window. Things have a tendency to fail in strange and unexpected ways.

Worse yet, many people have older iPhones with outdated Safari. You can't tell them to just install another browser, because under the hood Apple mandates that all other browsers are still the same outdated Safari engine.

If you want to track these issues down, you need to invest in an Apple based set up. You can't run Safari outside of the Apple ecosystem to track these issues down. It is bad enough that people are now offering pay as you go Safari instances for testing. Apple gatekeeps, Apple invents problems and developers are stuck with the bag.