This is not a comment on you as it is a reasonable question but I have wasted too much time arguing with Manjaro fans and I do not want to go down that road again.

To answer the question partially, there were two classes of problem:

1 - governance - this includes the stuff like not renewing certs and not testing core packages. My system became unbootable more than once and one of those times I was not knowledgeable enough to recover and ended up reinstalling ( mostly a skill issue in retrospect ).

2 - package delays - I found more than once that the delay in releasing packages caused problems with the AUR. First, it sometimes meant I could not use AUR stuff because of missing dependencies ( like when that was the only place you could get dotnet - now in extras ). That was frustrating but not destructive. Worse, delays sometimes caused AUR dependencies to get installed instead of ones from extras or community ( because they were not there yet ). This happened with newish software or with packages that had been renamed or refactored. Once the AUR packages had been installed, they would sometimes stay even after the packages appeared in Manjaro repos. Then sometimes the AUR packages would disappear ( be abandoned as they had been moved into the core repos ) and I would end up with packages that would not update because of dependencies or where I would end up using source packages that took forever to build ( because git versions were the only ones available ). I thought all this was just the nature of the AUR until I switched to Arch it stopped happening. I have installed Manjaro since and had it happen again. I do use the AUR heavily.

Sorry, I ended up saying more than I wanted to. I wanted to answer your question but I do not want to argue. Honestly, if Manjaro works for you, I am very happy. If you think I am wrong, that is ok. I wish you luck.