Engineer group orders is a good idea. Can we reduce the diminishing returns on assists though? I'm not asking to eliminate them entirely. If diminishing returns is 50% productivity for each additional engineer, the most you can get is double (1+sum (n=1 to n=Inf, 0.5 ^n) = 2. I think a better number is 75%. At most you can get 4 times the build rate (1+sum (n=1 to n=Inf, 0.75^n) = 4. But at a more reasonable number, say 5 engineers, your build rate is 3.05. 3 engineers is 2.3.
I think 0.75 offers more strategic and tactical options for how someone chooses to run their economy. It will open up several viable "builds". It will make the storage techs more enticing as people will have more opportunity to burst build as needed. It will better allow radical shifts in strategy to changes in map conditions, it will allow a player to set up defensive stands better if they find they have neglected a part of the map. The streaming economy still limits how fast you can do things.
Perhaps let us play around with 0.75 in patch 0.95 so we offer feedback. Thanks for your consideration.