This kind of analysis doesn't always work. Takes aeon labs : they have better dmg/mass and equivalent hp/mass compared to aurora. Just taking those into consideration you would build labs only and never auroras.
But things like speed, range, having more concentrated hp, alpha strike, better turn rate or better turret actually do matter a lot when comparing two units.
You should make some tests with someone else where you fight mass for mass inties vs swifties, and you'll probably realize it's not completly unbalanced towards inties.
I wouldn't say that shockers are useless ... But a small +50 damage boost could make sense yea, it would cement their strenght vs the obvious weakness of having less AoE.