As far as AUR is concerned, one should be fair. The things that are offered in AUR can be problematic in general. No matter if you use vanilla Arch or a distribution based on Arch. Because not everyone who offers something in the AUR cares about updates in a timely manner or at all.
With Manjaro, I rather see the problem that the team responsible for it apparently does not learn from its mistakes, so that, for example, the SSL certificate of the website has not been renewed several times (web.archive.org/web/…/manjarno.snorlax.sh/). That may not be a big problem in itself, but if even such little things go wrong, then I personally cannot trust an entire distribution.