Nobody's perfect, all Linux distros out there have had a rough start. The ones that endure and stick around are the ones that eventually improve. If you were around when Arch came out you may recall very similar attitudes from fans of other entrenched distros disparaging their efforts. Arch wasn't born perfect either, they made plenty of mistakes in their early days.

But if you'd demand perfection all the time you'd never use the vast majority of distributions that are trying something new. We need to rise above partisan and petty differences because Linux is a hotbed of innovation and freedom and we as a community need to encourage and nurture trying new things, not dump on it.

This is most importantly true in terms of delayed security updates.

Security updates aren't delayed in Manjaro, they're pushed through out of band.

You also don’t understand how the AUR works in conjunction with outdated Manjaro packages, which will cause dependency problems and lead to breakage.

Once you've compiled an AUR package it will remain compatible with the system you compiled it on until you update and introduce an incompatibility.

This is true for any Arch or Arch-based distribution. It has nothing to do with when the distro updates packages. It's purely a coincidental factor of whether a particular AUR package breaks binary compatibility with any particular distro update. Users who don't regularly update their AUR packages to keep them in sync with the system will seemingly randomly experience breaks, depending on what AUR packages they use. It can and does happen on Arch just as well as any derivate distro. You need to either automate AUR updates or update them by hand to avoid it.

you can read what Arch’s security team thinks about Manjaro here

That's not the "Arch's security team", it's one person on a 3rd party forum, with a history of issuing personal statements reeking of personal grudge. Yeah I know that comment unfortunately. It's a singular, isolated piece of flamebait and it makes me sad to see it's still being bookmarked and passed around 5 years later.