I don't think Watts was the first riot of its kind. While the earliest race riots involved Whites attacking Blacks, Harlem had already seen disturbances of the sort that erupted in Los Angeles in 1965. The problem with debates about deeper causes, is that the most relevant factor was the behavior of the police. In general, you don't need massive programs or large scale changes to prevent such riots. You just have to make sure the police are well-equipped to deal with disturbances and do their job fairly and effectively without sparking such outbreaks.
See these:
NY Times headline search for "Harlem riots" (results = 1870-1974)
The Root of the Trouble (editorial, Jul 23, 1964)
The headlines show your list of riots, racial or otherwise, in Harlem over the years. In each, police behavior is cited as a cause, and, as far as I can tell from the survey of headlines, absolved in the specific in hearings and reviews. The '64 editorial gives that year's problems to, in ascending order of importance, radicals, police, and poverty. Call me naive, but I'm thinking that the role of the police is far more reactive than causal.
I think it all rather affirms McWhorter's view that the radicalization of the civil rights movement did nothing to resolve the crises, and that the crises were less drastic than presumed by apologists of the riots. Certaintly, everyone agrees that better economic conditions were the fundamental cure. McWhorter seems to say that that solution was well on the way prior to 1968, and was halted, so far as the inner city goes, by the welfare state. Wilkins punts when he takes on McWhorter on this point:
...And Watts and the explosions that followed helped fuel a conservative backlash that undermined the massive effort needed to address the problems it exposed.He's kidding himself. You think he could learn anything from Booker Washington?
The Watts legacy is not about tinkering with welfare policy. As the Kerner Commission warned us 2 1/2 years after the riots (a warning soon to be all but forgotten), the problem comes from a place deep inside the American soul. The profound damage done to unlucky blacks trapped in poverty and to whites trapped in indifference or bigotry will still require an enormous amount of sustained American will and decency to correct. That is the real legacy of Watts.