Pro cameras were not developed for the "prosumer" but for the real "pro" as the product marketing states accurately. Yes, prosumers rode the coattails, but did not drive development. More than that, Canon subsidized photojournalists and Nikon involved them in product development. They were extensively used in ad campaigns (YouTube) where the pro photog becomes a celebrity in his own way (always a guy) and uses the advanced features; that's called downselling (aka pimping in adspeak). That still doesn't mean the feature was developed for prosumers; it just means they take a pro feature and shove it down a price point to buff up margins. It's still done today in many product categories (autos, golf clubs).
A lot of this was tied to the increased use of positive film. Kodak and Fuji loved things like bracketing because it meant more shots. It became part of their financial profile for the product. Positive film's narrow latitude pushed exposure accuracy into the camera on a more automated basis, spurring the # of shots per opportunity. Excellent for biz if you sell film. The perfect positive reinforcement feedback loop driving margins. It's a business model unto itself and part of the synergy between the camera makers and the film manufacturers.
That's all broken now.