I installed Arch on a disk without erasing the /home partition that cames from a previous distro. It saves me some config work, and a bit of disk life expectancy I guess.
Flakes is still experimental. NixOS devs takes a bunch of time to release that. So most experienced users have enabled Flakes since years. Two different systems are available, which does not help ease of learning.
Glibc has extensions that fragment compatibility. If Glibc is replaced by another libc, some apps prints an error, or don’t work. I noticed that on Alpine.
For me the main config difficulty is from the statusbar. Polybar, Eww, are harder to config comparing to the WM. I solved that with Tint2 bar. It can be configured from an GUI, for the basics. The only code I added to config is simple.