Jester David
Hero
*shrug* I could be wrong. You'd think I was human or something.Huh? The Temple of Elemental Evil - elemental cults par excellence - is discussed in Worlds & Monsters.
Ogremoch and Imix, plus their cultists, are statted in MM3. Yan-C-Bin is statted in one of the magazines - I don't remember which one, but I've used the stats.
In other words, what you say is manifestly mistaken.
And my feeling is that incorporating the other 5e APs - if one felt so inclined - would be quite straightforward.
So you can make a case for 1/5th of the APs. Still far less than the "all" of the OP.
Even then, PotA fits the PoL as much as the Realms. Nothing is gained by swapping setting.