Does the 1~2 week delay improve Manjaro stability over Arch?
I run Manjaro on the computer I use 99.9% of the time. It's been rock stable but there have been a few issues, over the years. I've been forced to reinstall on four occasions, since 2017. I expect it would have been more but I stopped taking updates until a week or two after they are offered. Every issue could have been handled with timeshift but I only started running timeshift about 6 months ago.
I also have an Arch laptop that I use a few times per year. It's been very stable but it goes for weeks without being used. I have no way to know how many problems it would have had if I used it every day.
Any thoughts on which is more stable? Maybe it doesn't matter that much, with snappy and timeshift?
According to Debian users, "stable" means "unchanging" and not "doesn't crash or have bugs" ... If you still ship 100% of the changes but just delay them by 2 weeks, you have the same number of changes. So by the Debian definition of "stable", no, it is the exact same as arch.
By the everyone else definition where "stable" means "doesn't crash or have bugs", then also no. Shipping buggy code 2 weeks later doesn't reduce bugs. And if you use the AUR at all, then things get worse, I've found, as the AUR pkgbuilds expect dependencies to match current up to date Arch repos.
tl;dr - no