"The brain behind AMD Ryzen" is still working for AMD and just published a paper on an outer product accelerator to go along with AVX10 a couple weeks ago. TT's CEO Jim was upper management at AMD during Zen and got rid of a lot of useless managers while Zen was being designed, but Zen was already in progress before he joined the company (this is his words, from a public podcast).

If anything you should be excited that Wei Han (who was a heavy contributor to the Apple M1 architecture) is the head of Tenstorrent's RISC-V Architecture team. He's far closer to making key architectural decisions than Jim has been for decades. Not saying Jim doesn't have his finger on the pulse, he does, but he's far from being "the brain behind" anything - he's the brain behind getting that shit funded though, which he is very very good at and is arguably a more difficult task.

But Jim is still doing what he does best, and what is arguably more impactful to the end product: firing useless managers.