Epic Games tried side loading Fortnite on Android, and then went back to the Play Store. Here's their statement:

Google puts software downloadable outside of Google Play at a disadvantage, through technical and business measures such as scary, repetitive security pop-ups for downloaded and updated software, restrictive manufacturer and carrier agreements and dealings, Google public relations characterizing third party software sources as malware, and new efforts such as Google Play Protect to outright block software obtained outside the Google Play store.

So basically, the fear mongering about major publishers taking advantage of sideloading is entirely unfounded, which is exactly the point I was trying to make.