Unlike iOS where basic features like the web browser require system updates, Android is modular and updates get pushed through other channels independently of the OS itself.
Yes I'm aware of WKWebView and how it's not the same as Safari. I'm using the classic meaning of browser skins, dating back to browsers like Maxthon which were wrappers over Trident in exactly the same way.
It's similar to complaining about other basic features of iOS IMO (like complaining there's a default settings app or that iOS just works a certain way).
Think of Safari as a skin that's unbundled from the engine. While Chrome or Firefox are reliant on Apple to update the engine, so is Safari, but neither are reliant on Apple for other functionality that they want to implement that users can take advantage of.
IMO it's modular enough.