Does it make me a bad person to steal the NM when they wipe and then kill it in 15~45 seconds?
Only if you think killing it fast is any indication of skill, not hard to destroy an NM with easy to get gear and atmas. Ukon war is broken really and easy as pish to get and gear, I have 90 Ukon and can mash down NMs fast with it but I'm under no illusion that I'm an awesome player for doing so.

A lot of other people don't have these things but they are still laughably easy to get, on the positive side for OP we are getting 95 soon and that will make people soloing NMs able to kill them a lot faster.