I totally agree. If you're on a proven High Sierra system and have all your apps installed, you can wait. But unfortunately some (including me) were just installing a clean new system coming from stable Sierra system. So there I had two options: going back to Sierra, or trying to workaround the issue, at least until Cupertino has fixed the problem (I hope they ever will somewhen).
The problem is definitely in the AMFI, a security check integrated some years ago. I found an explanation about this security subsystem there: https://eclecticlight.co/2018/12/29/amfi-checking-file-integrity-on-your-mac/
I think with the last security update, they broke something in the AMFI. Therefore the only possibility is to deactivate the whole AMFI, until they release a bugfix, if someone want to stay on HS and need to download apps from the App Store.
The problem is definitely in the AMFI, a security check integrated some years ago. I found an explanation about this security subsystem there: https://eclecticlight.co/2018/12/29/amfi-checking-file-integrity-on-your-mac/
I think with the last security update, they broke something in the AMFI. Therefore the only possibility is to deactivate the whole AMFI, until they release a bugfix, if someone want to stay on HS and need to download apps from the App Store.