3.X gave uncapped advancement. It also gave stats for gods. Which led to the inevitable eventually of there being a priest of Zeus (for example) who could beat the everlovin' crap out of Zeus. In fact, by about 50th level, a character should have had pretty much any god that was given stats in 3.X praying to HIM.
I'd say that depends on the portrayal of the gods. I could argue that if you've got a 50th-level cleric, clearly whoever the god is of that 50th-level cleric is just a wee bit more powerful than the cleric.
This isn't a problem with uncapped advancement. This is a problem with giving deities standard NPC statblocks.
Fortunately for everyone, Paizo has solved that problem by stating unequivocally that deities do not and will not have stats in Pathfinder, because they aren't intended to be direct combatants that the PCs can fight.
As such, no matter how powerful a priest of Zeus is, Zeus can always be said to be stronger, because he doesn't have any stats that say otherwise.
Exactly. And in some campaigns (e.g. mine), Zeus would stay that way. Yet in others, the PCs might one day kick in the door of Mount Olympus, kick butt and take names. In that campaign, that GM would stat up Zeus. And I'd cheer, and say "yay, you had fun!"
Even though it's not something I'd personally do :)
I'd like to see an epic level adventure and a sourcebook to support it. I want to see what paizo would do with such a thing and would happily buy into it. It might even get me to start up my AP subscription again.