You are right, multiple threads have been created on this subject, and ive supported for increased responsivness in every single one of them,
About the discrepancy, from what ive noticed its more the actual shot or projectile taking time to do damage rather than it doing damage before it hits.
Lazers for example, in theory a unit should already be dead but its being targeted by 10+ lazer units, its only after awhile that it receives damage and explodes.
Turrets, they shoot their projectile, the projectile hits, and only after awhile will you see the hp for a unit decreese on the tooltip.
Im not sure if this is a latency issue? or some kind of performance trick to help in rendering explosions and unit deaths. But whatever it is this seems to create an overkill issue on a lot of units, which is something armies and meta units dont even manage properly, and i doubt they will ever will.