I respectfully disagree Chris.
While different authors have had different perspectives on the matter over the years, I can think of enough examples where it was pretty solid that (at least on their native planes mind you) archfiends were a notch above a deity who also happened to make their domain on that plane.
We had Gruumsh and Maglubiyet evicted from Baator and dumped into Acheron because the squabbling of their petitioners drew the ire of the Lords of the 9. Khin-Oin the Wasting Tower was carved from the spine of a god killed by the 'loths. The early history of the Blood War involved gods on both sides, till growing tired of deific hedging in on "their" genocidal conflict, every single god involved began to have their deific essence fragment and decay, till one of them abruptly and horribly died, at which point the others dropped their involvement like a hot potato. And there's another instance [see 'Hellbound'] of a god killed slowly and agonizingly by the wholesale slaughter of their worshippers, and the suffocation of their faith, on a planetary scale by the fiends.
Plus for a more recent example, Lolth seems to have ended the edition struggling to secure the borders of her deific domain in the Abyss and prevent Demogorgon and Zuggtmoy from ripping control of layer 66 away from her.
Certainly I side with the perspectives that some other writers in the past have had: the fiends are the true rulers of their respective planes. Gods like Lolth might have an evil alignment, but the archfiends are the physical manifestations of Evil. Call it home field advantage if you want. Outside of those planes however, and certainly on the prime material, they're at a distinct disadvantage to gods who don't have their power supplied by (and apparently anchored to) their native planes.