I mean, it's not really Blizzard's fault outright. How do you truly display situational bonuses like single Skill bonuses? Elemental bonuses? Elite only bonuses? Granted, there should be a better advanced set of stats to display these but the Damage value does a "decent" job of representing most things. It has some bloat in it still (IAS% primarily) but it's "good enough" as long as people are aware of the other multipliers working behind the scenes so to speak.
Speaking of, give me a fucking training dummy in town or something. I mean, I guess Ghom is basically that but still.
They can at least add those multipliers in the detailed damage tab that pops out on the side, now you just need to track it in your head.