M1 was built by the PA Semi team, acquired in 2008 [0]. They build the A series chips in the iPhone, I would argue that M1 would not exist without them, furthermore, M1 was not a Cook endeavor. For the watch, it looks like the first key hire was in 2013, but there is a chance that it was not all Steve's work [1]

0. https://en.wikipedia.org/wiki/P.A._Semi 1. https://www.wired.com/2015/04/the-apple-watch/