Weaknesses of Arch

 * It's "KISS", not in the sense of keeping engineering simple to avoid bugs and making things simple to understand but "KISS" in the sense of keeping it simple for the developer. Arch seems perfectly fine with including complex pieces of engineering that are known to oftentimes bug out, as long as they don't have to write them themselves. Someting like Void or Slackware is KISS in the former sense which leads to both systems being rock solid and typically devoid of bugs.

 * I really dislike how Arch' packages are extremely large and how many things they dump together in one package. They don't split library from interface in packages or runtime libraries from their development headers, the latter of which typically being larger than the runtime library itself and almost never needed. Other systems split this off to avoid having unneeded things on your system

 * "partial upgrades are not supported", as it stands I lie partial upgrades a lot and I hate to be forced to upgrade thing X in order to upgrade Y. If I want to keep X back and upgrade Y I'd like to do so.

 * The entire system is devoid of policies, the developers basically make it up as they go along and change things when the want with no promises for the future. A lot of systems have strict public policies they adhere to so you know what you can expect when you install

 * Arch' official repositories are super small compared to most systems, people often praise how large the AUR is, but that's a necessity beause you have to use the AUR for things most systems have officially maintained packages for. And the AUR is still a minefield, any maintainer of a popular AUR package could troll all its consumers at any point and just install spyware or whatever

 * Pacman is unsafe, package scripts run as root and can do anything they want.

 * Arch is in general kind of a system of "good enough" as in they are perfectly willing to let race conditions and other things continue to exist which are sufficiently rare that it's "not really a problem", this is also how they encode dependencies in packages, not encoding a lot of dependencies and above all correct versioning because "Meh, 99% of users will have this package up to date enough"

 * Due to the above, Arch can become unupdatable if not updated for a specific time. And since there are no policies it's unclear what that time is. But typically if you come back after 3 years to an Arch install and do a world update it'll fail and throw your system into a malformed state which it can't recover from. They say you should "frequently" update, but how frequent, no one knows really.

 * Arch doesn't really support a lot of things like SELinux or other such stuff

 * Arch has no policy regarding acceptable licences and how this is handled or in general what software is acceptable in their own repos or anything like that.

 * Some Arch maintainers seriously put builds on a cronjob automatically and push it out to the repos when the build completes without error and automatically sign it, no human intervention to as much as check if it all went appropriately or any testing.