The bandaid treatment....
Could we please discuss the lack of thought process you really gave to artillery/poke mages? You've seem to given a small buff to there late game potential while reducing there early game power (xerath and ziggs specifically). It's not as if they were over bearing in lane early game....
Listed Problems:
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No keystone, honestly there is nothing that even remotely fits this type of play style for poke mages.
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Lack of mp, honestly suprised we didn't see more of a variety for the type of magic pen offered. Considering there are only a potential of 4 items of the game offering it (3 of the 4 viable for poke mages) and only 2 of them being really efficient...

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Reducing of ap on core artillery/poke mages items (not to mention lack of build paths you are giving us with the mana requirement early...)
End overall i think you are sufficiently setting in stone a passive playstyle early with a set build that they need to follow, perhaps i'm overreacting however i can't help but feel i'm being restricted....