It doesn't matter if the damage being multiplied is vaporize or her burst hp scaling, the extra 24% multiplier adds more damage to the total output than the HP% Prototype Amber can provide, which also gets diminished returned the better you artifacts is.

With my own artifacts 2pc HoD+2pc Maiden, Magic guide with its low attack can hit around 1000 per lvl10 aa (no burst) while prototype amber hits around 1200. However with Magic Guide's passive, magic guide aa does 1240 which overtakes prototype amber. This difference is even more pronounce once in burst. Burst aa with prototype amber hits 6600 while magic guide hits 7000. And all of these are not even factoring the 178 em and the extra damage it gives to reaction damage.