Regenerative braking is so far from being an innovation on Tesla's part. Regenerative braking as a technology has been around since 1886, and was even seen in some of the earliest electric cars at the end of the 19th century (krieger electric landaulet).
Even when you fast forward to modern production cars, the Prius had a regenerative braking system almost a decade before the Tesla Roadster came out.
You might want to check out "Elon Musk" by Vance on what his innovations were with the battery and drive system. Yes, people knew about regenerative braking. When was the last time someone built an electric car with regenerative braking? The Tesla was not built with off-the-shelf batteries and drive systems. Musk originally tried to, but they were unworkable.
Even when you fast forward to modern production cars, the Prius had a regenerative braking system almost a decade before the Tesla Roadster came out.