[998244353]

You're right that discoverability is not really the issue.

However, I still agree with the GP that if you are not on the Play Store, you lose most of your installations.

If someone has already discovered your app and can't find it on the Play Store, they are more likely to assume that it's not supported on their phone, unavailable in their region or whatever. Even if you explicitly tell them to just download the APK, most people will not do that. Keep in mind that the average user probably doesn't even know that you can install apps from outside the Play Store. Or even if they guess that it's probably possible, they might well perceive it as complicated and sketchy.

[grishka]

I don't understand how does one come to this conclusion. In my own experience, most people will do what you ask them to do as long as your instructions are clear enough. Downloading and installing an apk on an Android phone is no different than downloading and running an exe on a Windows PC, which is something people do all the time. No one perceives Play Store as inherently more trustworthy. I know many non-tech people who have and use sideloaded apps on their phones.

Edit: it might be different for younger generations who grew up with modern smartphones.

[Zak]

Epic Games can probably tell you exactly how many fewer people install an app that's not on the Play Store on their Android devices. That information might even be in public documents from their lawsuit against Google. That they were able to sue and win suggests it's large.

[rvnx]

+ Epic has visibility and audience already. So imagine if you are a developer without that.