I'm sorry but I have to break a lance in favor of Orpelith. Technically neutral territories are no man's land and therefore there is no law protecting those places, that's why he doesn't put his control in that place, more that there are mostly criminals and few civilians who don't want to live with giants (totally understandable).
Where Orpelith did screw up was in the creation of the guardians. Seriously that woman has a lot of confidence in that agreement "signed" by all nations. It is not for nothing that the "Geneva Conventions" are jokingly called "Geneva suggestions".
Do you really think that in a war they are going to follow those agreements?
I'm sorry if it's not clear but I'm using a translator.
The existence of no man's land called "neutral territories" in the first place is one of Orphelith's biggest crimes. If the status quo wasn't being enforced by Orphelith, the "neutral territories" would have become parts of kingdoms, and enjoyed law enforcement.
Or, what is much more likely, the "neutral territories" WERE parts of the kingdoms, but then were annexed by Orphelith and turned into lawless hellscape they are now.
And I don't even have to come up with arguments for the latter theory. Literally most armed conflicts in the last 50 years that were "solved" by UN intervention - were by creating the no man's land demilitarized zones, stalling the conflicts indefinitely and letting those wars smoulder forever. Just like "neutral territories" in GG.