Let's go with your point about "density" [[aka population) first. According to city-data.com, the residential population of the Downtown neighborhood [[which includes Bricktown & the CBD) is 4,359. Generous estimates by the Brookings Institute place it at 6,500.
See here for downtown population data.
The populations of those living within a half-mile of the proposed M1 Rail line, which would include some parts of the populations of New Center, MIdtown, Brush Park, Art Center, and Med Center, is conservatively 25,355. Remember, this is residential only.
Add the roughly 80,500+ people that work Downtown you have roughly 86,000 people that could potentially use the People Mover. M1 Rail, on the other hand, can tap into the additional 20,965 New Center employees, 12,000 Med Center employees, 2,500 Wayne State employees, and 31,786 WSU students, and suddenly the M1 can serve from 141,320-173,000 people conservatively compared to the DPM's 86,000