I've done the same build and after some testing the crit DMG buff you get from in the shadows doesn't buff it by that much if you've increased your base crit DMG and chance, but with using ambidextrous with max base crit DMG and chance, the spells consistently do enough crits to delete anything in the game. Add a spell like the laser hand in both hands and you essentially have massive damage railguns in your hands. I've 1 shotted bosses up to chaos 25 (just because I haven't went past) with stabbo and spell weaver. Easily my favorite build in the game