True, but iOS doesn't have OEMs having their own forks, which takes this to the same level as J2ME used to be.
Whatever they come up in GUI features, changes to AOSP behaviours, custom drivers, their own extended SDKs on top, hardware form factors,...
I certainly mean Android device I can buy in any European country from the lame 100 euros pre-paid throwaway phone up to 2000 euros three ways foldable phone, plus everything else running Android on cars, kiosks, TVs, handhelds and everywhere else Android gets installed as alternative to GNU/Linux by OEMs.
CTS only covers a subset of what everyone is doing with Android.
And it will never cover everything, because as the Android team likes to point out, they don't want to stiffle the innovation of their partners.
You wish. Xiaomi is especially popular in Europe and has countless specific bugs. This "certification" does nothing.
If you mean Chinese or Russian OEMs with their own version of ASOP, well that's not really Android anymore and is not using the Play app store anyway.
Western devices have to go through certification to use the name Android, so its not the wild wild west you think it is (although obviously some bugs may fall through).
See for example
https://source.android.com/docs/compatibility/cts