One of the early developers of regenerative braking, justin Le of Grin Technologies, has said one can get up to 10% recovery in hilly regions. Nice if you live there and have to use brakes to control your downhill descents. Where I live, I might get 20 mph coasting down a hill for 10 seconds, and the hill is over. And I have to have a direct drive motor too.
Meanwhile, battery improvements have been pretty good in the six years I have been ebiking.. I just bought an 18AH battery for less than what I paid for a 10 AH battery in 2015. That's like 80% more range. I've got more battery than I need for a ride these days,
As Cat0200 points out, having a bike dynamo capable of charging a phone is like riding uphill 24/7. Why would I want that penalty on my biking.