Google Chrome is Google's master plan to remove responsibility from the Operating System and put it into their full control. Of course, they have operating power to move forward 300 APIs at the same time. However, they do it with the main propose of governing the ecosystem where those APIs are pushed (the web).
The only way to be up to date with all those changes is power (operating money).
Firefox is barely able to catch up with all the updates to the standards... there is obviously a burden on what is needed to be implemented for a browser in 2020 vs what was necessary 10 years ago.
However, Apple argument is not about delivering value to their users via a browser, since that's an ecosystem they don't control. They deliver value through their macOS/iOS SDKs, which are ecosystems they fully own. Apple moves Safari as minimal as possible (regarding new APIs added) to make sure people can still browse, but while still incentivizing their own routes.
This kind of API strategies are everywhere the software touches. From Apple moving Metal forward instead of Vulkan, Microsoft with Directx12. Google with Flutter (towards cross-platform API UI dominance) and so on.
I don't think is a question of what the companies want, but what do their users use. As long as Safari is the dominant browser in Apple's ecosystem, they will make sure you can max out the value received through other ways that align more with their vision and proprietary APIs.
So, if you consider "Web" what Google is pushing on now, it's clear Safari is not pushing forward in that ecosystem. But none of them do it for the sake of their users, but their ecosystems