Planar Alignment and Exemplar What-ifs

Actually, Gray Waste is suffering, if you look at beings such as the Oinoloth. IIRC there are other embodiments of physical pain and pestilence on the Gray Waste-- apathy is another form of suffering, and even the Oinoloth is hardly immune to it-- he is diseased *though it does not cause physical pain*, disillusioned, and left behind by his bretheren-- he represents the old and obsolete paradigm of the Yugoloths to cause primordial versions of suffering-- pain, pestilence, apathy, as opposed to the new paradigm, which is intrigue and manipulation. Of course he is still central to the Loths' ultimate plan, but beyond that he has taken a much lesser role due to the migration to Gehenna and the paradigm shift.
If you look at what a neutral evil being truly is at its purest, I would say that the Gray Waste also embodies selfishness, even if Gehenna and Carceri better fit this description (the hags certainly fit it to a T) (I like to call Neutral Evil "Neutral Selfish" BTW, just like a lot of people like to call Lawful Good "Lawful Stupid" and chaotic evil "Chaotic Stupid")

Gehenna's theme would be malevolence, not suffering (remember that everyone and everything on Gehenna is out to get you just for the lulz) This is not the same as what is found on Carceri, as malevolence does not fit the description.

I think there should be a better term for Carceri, though I can't think of one at the moment.

The abyss is Anarchy/Mayhem (I include the slash and second word to clarify which definition of anarchy we speak of. It is not the same as the form of "anarchy" found on Limbo, and Limbo should not be summarized as "anarchy", anyhow, as its form of chaos generally does not encorporate the mayhem associated with rioting, even though riots are certainly common on Limbo, I would not categorize them as everyday occurences like they would be in the Abyss.)