Anyspell cannot be used to meet arcane based PrC requirements, also when you get down to it items are not intended to meet PrC requirements either.
I agree about the items, but why can't Anyspell be used (in any situation) according to you?
FAQ ruled Southern Magician doesn't qualify for PrCs based on the grounds the your spellcasting ability is still X even if you are casting a Y typed spell. Anyspell likewise says when
you cast the spell it is treated as if X cast it, well since you can't cast arcane spells you're using your divine ability which is mechanically similar to Southern Magician.
A second point to add to things is the FAQ's ruling on Southern Magician provide a clear point that when PrCs use the word ability they are not talking in a general English sense. This concept is enforced a second on the very same page as it touches on the interactions of Domain Spontaneity and Reserve Feats. Where even if the outcome is a measure of spontaneously cast spells, even Reserve feats only acknowledge your real ability to cast spells and not half-assed alterations to the outcome of what spell can be produced.
A less factual point but third point would be using UMD to meet PrC requirements. The end result is a spell being cast and you made it happen so in a general sense you really do have the ability to cast spells. But when you get to handling the rules,
ability is a more specific than that and this is understood well enough by many DMs, including RGPA ones, as not to include UMDing stuff and it isn't allowed.
The is what the rules indicate towards Anyspell cannot be used to meet arcane based PrC requirements. The only thing that opposes it is a language debate where someone is explicitly operating as
if the dictionary was the one and only true definition. So like all language arguments it's not about the original subject, but proving that they are right if things were exactly as they claimed them to be. E.G. Trolling.