@FtXCommando I really dont see how. Like, ACU is you primary defend unit, and when you upgrading him, you cant walk and defend your base.
To do it, you have to make a lot of units (presumably T1, cause T2 is too expensive), which is also costs a lot of mass. And it will be okay(mostly), if not T2 rockets, especially when they are coming from above where T2 patrol are going.

I will soon go throught replay of @Nomander, want to see how)

@FtXCommando You dount have enough mass to upgrade ACU, and furthermore, you dont have enough time to do it.
Tried like 10 times, no way to beat without cheats or mods

Its totally unplayable on hard difficulty, by all means, you can start developing your base at the last breaths of ACU, but not when T2 rhinos coming from nowhere with T2 rocket launchers and you dont even have T2 air or T2 shields/defence weaponry. And at 20th minuts author literally joking I assume.
I mean only 3+ players can win this, when giving all their income to the one and do nothing but defend this one with their ACUs