the spell makes you believe the illusion is a real thing. just because there's an illusion of "king so and so" doesn't mean that the target must believe that it legitimately is king so and so, as opposed to someone that looks like king so and so for any variety of reasons. they won't believe it's not there, but they can believe whatever else they want about it.
PF makes the target believe the spell is a real thing. it doesn't make you believe that the thing over there is a real avatar of a god, it just makes you believe that the thing really is there. it could be some sort of puppet, a big creature disguised as the god, or whatever, but the thing is, unless corellon larethian makes a habit of traveling around the world smiting random small groups of orcs, you have created a scenario where "this thing is obviously something trying to trick me into believing it is correllon larethian" is more reasonable then "clearly corellon larethian has decided to show up and fight half a dozen orcs in the middle of nowhere".
now, if you're in the main temple of corellon larethian that is currently being desecrated by orcs, it would be a bit more plausible that the avatar of corellon would show up. but again, nothing forces you to believe that the illusion is the real avatar of corellon larethian, it only requires you to believe that the thing really is there. it isn't a charm or a suggestion, it's an illusion.