Re: Not using Chrome as the Android default browser...
WebView pre-dates Chrome on Android by several years. In very recent versions of Android (just Lollipop I think), Chrome has now replaced the WebView component, but this change has not been applied retrospectively.
As you point out, increasing numbers of Android components are being moved out of the core OS and into "Google Play Services" allowing Google to push updates and fixes to older OS versions without involving the carriers, but this is a gradual process over several OS releases.
Which is not to defend Google's actions in this situation, but at least they seem to have identified the underlying problem and are moving to address it (albeit slowly). I'm guessing that some people at Google have been getting something of an education over recent years in the difficulties of supporting a mass market operating system running on diverse hardware supported (or not) via various OEMs.