From that very statement " if they also exist on the playstore ". Sideloading entirely can get you around this.
Sure but realistically speaking, don't you understand the fundamental problems at play here and why this runs into similar issues that caused Microsoft to lose to Netscape?
One of the reasons Microsoft lost is due to their outsized ability to influence what people perceive to be their options.
When people look for new apps to download, first and foremost they will think of the Playstore and iOS store respectively and give the alternative store of the company that built their phone a second thought.
In this case the playstore isn't being used to prevent people from sideloading but Google knows they can force sideloading developers to use their payment processor exclusively because it is much harder to market the existence of your software without also being present on the playstore.
So in this case google's violation isn't about the software developers who side load but about the payment processing ecosystem.
Google has several problems unlike Apple and this is the most obvious one where they can lose.