Pants said:
I'm probably making generalizations here
Yes, you are. It's not a "just another monster" issue, it's a matter of internal logic. If the lords of the underworld are only CR 30 or so, how the heck do they avoid being conquered by deities? When Kurtulmak can finish Asmodeus off in a few rounds and teleport away, something is very wrong with the cosmology. Why hasn't Demogorgon been slaughtered by rival gods of the aquatic races? How did Pazuzu manage to curse the entire race of kenku, as described in the recent Dragon ecology? How did the Lords of the Nine banish the orcish and goblin pantheons from the Nine Hells?
In 1st edition, fiendish rulers were all lesser gods, and most of them were of a similar or greater amount of power in 2nd edition. That made a certain amount of sense - even Bane would hesitate before taking on a plane ruled by nine lesser deities. In 3rd edition, all semblance of sense is lost - the rulers of nine infinite domains are vermin, less than that. Vhaeraun can march into the Gray Waste and give orders to the Oinoloth, as he did in a recent drow-themed novel.
Evil deities are
not the types to make peace treaties if they don't have to, nor are they the normally the types to cower in fear of what the other deities might say - it's inevitable in the cosmology implied by the current rules that someone stronger than the rest is going to take control, and the eons of self-rule the demons, devils, and other fiends has enjoyed is gone forever.
And that's fine, if that's what you want - a multiverse where Bane or Hextor rule the Nine Hells and Cyric and Talos or Erythnul and Raxivort are the mightiest of the lords of the Abyss. But, I mean, if Raxivort and Iuz are both mightier than Graz'zt, why is Graz'zt still alive and not serving them drinks in a French maid's uniform?
The common retort I hear is something along the lines of "the other deities would all turn against anyone that threatened the status quo in the lower planes," but a campaign where evil deities don't threaten the status quo (especially on the chaotic planes) sounds like one where evil deities aren't doing their jobs. And who really loves Graz'zt so much that they'd object to his son or former servant taking his place?
I think it's completely fair to criticize a cosmology that's poorly thought out. James Jacobs' fix of making the stat blocks into avatars is fine - but it's still weird to see the default assumption be the least reasonable one.