Google is helping us is only because their ultimate goal for Android from their POV is get as much Gapps onto people as possible, everything else is secondary with the responsibility better off pushed to others, like the testing and validation crap. I doubt they even care about existing fragmentation of the Android user base as long as Gapps still work.
This doesn't make any sense at all. The entire strength of Android is that Google controls the base platform and OEMs can customize it to differentiate themselves. Google certainly handles the testing and validation of stock Android and honestly has about the same QA quality as Apple (which is to say decent but not amazing).
OEM customizations get us things like multi-window, double tap to wake, knock unlock, aggregated content feeds (e.g. Blinkfeed), mSD vs no mSD ,removable battery vs fixed battery, curved displays, all variety of display sizes and UIs- you can go on forever. Whether you care or not about each of these features doesn't matter - it's that you can pick the combination of features and UI that appeal to you the most.
Google being a bottleneck to build, test, and distribute all the OEM added features would basically eliminate all variety simply b/c it wouldn't scale. Apple has one UI and set of features - and they do it extremely well - but there is no choice and the extent of customization is basically wallpapers.
Having them both operate with the same model would be such a waste for consumers.
And of course a company builds products to benefit themselves - is Apple building iOS for some altruistic reason?