There's a lot of reasons people hate on Manjaro, though generally they boil down to instability - despite being on a slower schedule than Arch, a lot of people report worse breakage; their main "testing" is just being a week behind Arch without actually testing much.

Crucially, this can break things when mixing in AUR packages since those are shared w/ Arch and so anything in there that's precompiled against the Arch version of relevant libraries might just break.

It also has considerably deficient security policies, such as the GUI installer pamac allowing unsuspecting users to trivially install unvetted packages from the AUR without even a clear indication they may be dangerous, and they forgot to update their SSL certificates twice edit: five times (see https://lemmy.ml/comment/1343440), asking users to manually overwrite them as a "fix".

Unrelated to desktop, I've also noticed Manjaro staff are quite hostile and unpleasant to work with; I'm involved in a project that works on Linux on mobile devices, and Manjaro's mobile team has been less than the most pleasant. This is a personal gripe for sure and unrelated to the distro itself, but if I'm going to take a dump on Manjaro I'll do it all the way.

As for your other question; you can simply copy the sway config file from the Manjaro install. Either mount the ISO and search there, or if it needs to be installed to populate the sway config, just install in a VM and copy it from there. Necessary packages should be relatively easy to find by just reading the errors sway spits out and googling them.

Arch is about DIY approach. Arch derivatives for "making it easy" are a joke because they defeat the whole point of doing it yourself