Wow. Have a marlin spike? You might need it since you are tying yourself in knots. Look - First you argue that the DACA are keeping the marginal students out. why? Because they DACA are perhaps better prepared and thus win admission over the "native" kid. If the DACA kid is more competitive, they don't take anybody's place. The "native" kid was not as competitive - not as well prepared. 

I've heard a similar complaint about Asian students. They are better prepared and are accepted in percentages greater than their population. No fair, eh? Face it - the DACA kid was selected because he/she had better grades, better extracurricular activities, wrote a killer essay compared to other applicants.

Capacity arguments are silly. "Gee - I wish I had gone to Harvard. I would have except some DACA took my place!" Right. If only...

You keep ignoring the fact that colleges are not over-crowded and just because you are not admitted to you #1 choice is not denying you an education.