Assuming these decisions are attributable to him personally, then he absolutely deserves the description "visionary". That said, he's made plenty of other choices I don't like, and also invested in plenty of silly stuff that isn't panning out for them. I don't really think Nvidia needs a visionary right now. They have the best business in the world and they just need to execute. Regardless of whether he deserves to be ousted, the company will be fine without him for the next decade at least. So a stock selloff is silly.
The common argument is, well 'x' leader has had success in 5+ companies! Surely they must be excellent visionaries. Firstly, no single person in their lifetime can possibly launch/aid enough companies to success to have a large enough sample size to prove they are a factor for success. Launching 'x' amount of companies is great but its still such a small amount that it cannot really demonstrate anything. Secondly, once you have had success once, you gain connections, wealth, e.t.c. that only bolster further endeavors that you do even if they are pretty bad ones.
Ofc, there are things an individual at the top of a company can do to make 'good decisions', but this is mostly just selecting the right people below you to delegate to (thus reading/spotting talent well) and listening to your data and people to get as much information as possible before making overarching decisions based on that. This is what I consider common-sense and what most people do in their day-to-day jobs all the way at the bottom of companies anyways, alongside all their regular hard-work (engineering e.t.c.). Upper management just has the luxury of only have to focus on the common-sense dull part; listen to incoming data, make obvious meta decision.
by being ousted from his own company and using his golden parachute while * being bought back*?