This is gonna be complicated.
A. Designations don't work like buildings. It would require some major fiddling.
How so? Designating already works fine with digging. You just have to designate what you want, then a build menu comes up where you select the mineral you use, and then the dwarves build. Or just select the mineral, and have a count down on the side until said mineral is gone.
Finally I don't think it would take that much coding to at least remove the maximum 10 constructions you can build at a time.
Maybe removing the maximum...but designations take effect immediately, and buildings require you to choose material. What? Are you going to have a separate command for each material?
Just...needs a lot of fiddlies that I don't think would be necessary.
B. It only helps certain things.
Certain things that can become tedious in the current format. Imagine digging like this, your fingers would be worn down to stumps.
C. After designating a line or rectangle of wall or whatever, you can instantly designate another; therefore, there is little benefit.
You don't have to hit the u h j and k keys five thousand times to make a pyramid. That's a great benefit on player time and my pointer finger.
A. How big of pyramids are you building?
B. How many players build constructions-reliant MPs?
C. Use at least two fingers, maybe three or four or all. It helps.
D. You do have a point, though.
D. It works fine now.
That is no excuse not to improve or add to things. It's like saying 'The Horse and Buggy works fine. Why buy a car?'
A. The horse and buggy has some advantages over cars. Ask any environmentalist, or someone who has to deal with rising gas prices. Just because the car is newer doesn't automatically make it better.
B. Maybe it does need to be changed, but designations are just the wrong tool for the job. Maybe a new method in the b-C menu that is similar to designations-but no, not the designation menu itself.