Re: timeframe?
I'm sorely tempted to say "since always", but you could do it at least from sometime between 4.x and 6.x[1], but even then (and now still) it is a bit of a faff:
- You need to download the .apk "from the interwebz"
- Then you need to toggle the "allow apps from untrusted sources" in Advanced/Developer settings
- Now you can click on the .apk and it will install the app store after a big scary warning
And, while not discussed in the article (likely also not mentioned in the class-action), many basic APIs (such as location IIRC) are google-specific and will only work with a device that comes with Google Play from the factory, modulo workarounds (3rd party reimplementations, getting a Developer Key to enable installation of Google Play on your non-google Android device); so your 3rd party store apps may have limited functionality
[1]: I bought my first cellphone in ~2015 (A mid-range Huawei), and installed F-Droid on it (3rd party store with FOSS apps)