I don’t think this will be the case. Android has always allowed sideloading, but how many apps are sideload only? It’s basically just Fortnite and a bunch of open source apps. No major apps require sideloading because google play is still where people will look for apps and trust apps. Some commercial apps allow you to sideload from their website, but it’s pretty uncommon still.
And for consumer benefit, if you believe in free markets, developers not having a 30% overhead might end up forwarding those savings on to the users. It’s pretty common for subscription services to charge more on the App Store than they do on their own websites. And for indie developers, I’d rather they get a bigger chunk of the pie than give the world’s highest valued company ever more money.