Greetings. Yes, I do have a Masters in Composition.
I know that the GRE is not super important in music. but if you have a sub-par GPA like I do, then a high GRE score can help offset grades.
Also, some committees use the GRE score as a way to "weed" out applicants.
The most important aspect of the comp application is the music. But as you said, it is very subjective. Some schools look for very complex rhythmic music. Others like jazzy stuff. Some prefer heavy electronic or electro-acoustic music. I chopped good schools off my list because they were really into electronic music, I write purely instrumental music.
Most schools like complex music (like you said, tuplets inside quintuplets etc) But this isn't always the case.
Some schools like to see accomplishment in regards to competitions, awards (the only awards I have come from the University I studied at)
Sometimes it is very political, if you have connections with a University before applying, this can increase your chances of getting accepted, just like with jobs.
The whole point is that this process is a complete crapshoot, especially for composers. We don't have publications and specific research goals that fit perfectly with different schools. Everyone writes different music, so it is virtually impossible to find a "perfect fit"
Good luck to you with your applications/interviews