Of your three examples, only the Tech Center housed jobs that were at one time located in Detroit.
[...]

Chrysler's Warren Stamping was part of the new greenfield manufacturing complex that was constructed in the late 1930s to stamp and assemble the increasingly popular Dodge trucks, since there were no similarly-sized parcels available with the right zoning and rail access in Hamtramck or Detroit. For much the same reasons, the GM Warren plant was originally located and built to manufacture artillery shellls for WW II. It was originally operated by Hudson Motor Car and later on, GM took over the plant to build those shells, along with Hydramatic transmissions and other automotive metal components.


OK, but that just reinforces the point I made earlier that disinvestment in Detroit began as early as the '30s and '40s. Just for curiosity's sake, I did put together a list of auto factories built/opened in Metro Detroit's suburbs during the '60s and '70s:


Ford
Michigan Casting Center/AutoAlliance International [[Flat Rock - 1972)
Romeo Engine Plant [[Romeo - 1973)
Van Dyke Transmission Plant [[Sterling Heights - 1968)


GM
Romulus Engine [[Romulus - 1976)
Livonia Engine [[Livonia - 1971)


Chrysler
Sterling Stamping [[Sterling Heights - 1965)

That alone represents at least about 8,000 factory jobs [[obviously, employment numbers at auto factories fluctuate over the years) that the Big 3 located in Detroit's suburbs during the '60s and '70s. And remember. that list doesn't even include the factories built in other states and countries, which would have made for a sizable addition to the list.

8,000 factory jobs in Detroit would've meant potentially thousands of new middle class homeowners spending most of their money in the city. Things like that make a difference.

Also, uf we were to add in the factories opened in the suburbs during the '50s and '80s, that list would again be much larger. Now granted, you couldn't have fit all those factories in Detroit, but it's still evidence of substantial disinvestment.

And yes, we know - basing your economy on auto factories is a risky and foolhardy bet. However, the fact remains that if corporate investors would've supported Detroit more instead of the suburbs [[the factories are just a part of this equation), and if white flight wouldn't have been quite so severe, Detroit would've been able to weather the storms of changing economics and demographics much better.