Panetti's Replicating Missile, from Mastery and from Item

Hi everyone,

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I have recently purchased the game and am digging into a bit of the theory crafting as a new player.

I was wondering if the Panetti's Replicating Missile from the item Cortosian Scrolls is the same one as the skill from the Arcanist Mastery? If I put a lot of points into the mastery, will the procced Missiles get the bonuses of the Mastery points?

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Also, should you aim to max all res (at 80% ultimate) for an endgame character?

Thanks for your answers!