If you already using EndeavourOS, you are already using Arch. So it is a very odd question. You could remove the maybe 12 EndeavourOS packages and comment out the EndeavourOS repositories if you want to go truly vanilla Arch. Out of the 80,000 packages Arch makes available to you, about two-dozen are EndeavourOS specific. Once installed, they are effectively the same OS.
So, you are just asking if it worth it for an Arch user to move to NixOS.
From what I can tell, the killer feature of NixOS is rolling out a config to multiple machines. Is that worth a switch to you?
The other big attraction of both Arch and Nix is the huge package library but if you do not use the AUR today, that does not matter to you either.