There is no security benefit to Google's scare tactics of calling other companies "untrusted sources". Both because Google scans apps installed from untrusted sources on your phone anyways, and because Google's malware scanning is literally industry-worst: https://www.av-test.org/en/antivirus/mobile-devices/
Imagine if Microsoft made you enable "untrusted sources" to install Steam on a PC.
I see posts on Reddit fairly often where someone says that Chrome is warning them about going to Google.com. And then I see people "helpfully" telling them to just ignore the warning.
They're being man-in-the-middle attacked. And people are telling them how to mess with security, in a way that's completely harmful to them.
Messing with security so you can install a game is teaching you dangerous lessons. Shotgun aimed at face.
I agree 30% is too high. But this is not a good idea.