The repo delay is not the main cause of AUR warnings. While it can in theory cause mismatched dependencies for some AUR packages, in practice it doesn’t really happen that often.
The main issue with AUR is that it’s completely unregulated. Anybody can put anything in it, there’s no quality criteria, AUR scripts run as root and can do anything on your system, 75% of AUR packages were not updated during the last year, 15% were released once and never updated, and 10% are completely abandoned.
Arch itself doesn’t support AUR for those reasons. You should be wary of using AUR packages in general, on any system that can use them, always assume they can break at any moment, and never use them for anything critical.
It will fall through much faster than that. I’m thinking two years, tops.