For 3D item models on the hotbar, the viewport is cocked in a pseudo-isometric angle. Specifying "rotation": [ 0, 0, 0 ] (which should imply "no rotation") yields an object that is turned what appears to be 45 degrees to the side and 30 degrees down, instead of head on.

I understand that this pseudo-isometric angle was/is the default for blocks and I don't have a problem with that per se, but making it the hard-coded 'zero point' for all item models is annoying to say the least. These values SHOULD be written in the "/models/item/*.json" files with all of the other translation and scale parameters, instead of making people work out a correction matrix. Coupled with my other bug about rotation being broken (bug MC-72644) it's extremely difficult if not impossible to get things pointed where you want.