In the very early days of NT the GDI subsystem was in userland and you wouldn't have this problem. Unfortunately it was too slow for machines of the 90s and so GDI+user32 is very tightly integrated with the kernel.
Even to the point where it does neat things like callback user mode code from the kernel. Unwinding this without breaking things is nigh impossible at this point.
You have to put this into perspective with what they are replacing. You'd never get a submit done in less than 19 seconds using the old source depot tools anyways. When you work on projects this big that takes hours to compile and minutes to incremental compile - responsiveness just isn't something you get to have at scale.