He made some mistakes, but honestly, they overrate it way too much to blame it for Sega's downfall.
The truth is that most of his refusal were based on 2D games that died overnight in western sales with the 32-bit generation release, I sell videogames and most of the japanese Saturn software I have are anime niche genre stuff like VN that no third party would pick up back in the day for overseas release, the market was not there, not even the VHS anime adaptations. Was it necessary? Obviously not, just should have let go and pick royalties if anyone was interested.
The stance on the Saturn not being a future was actually a harsh truth by 97, Sega had done screwed up with the design that was mainly easier for 2D, Capcom which was a major Saturn and DC supporter had financial losses with Street Fighter 3 poor sales on the arcades and ditched out 2D games from their pipeline. He said in Arcade Attack interview that he only joined SoA if Japan could accept his demand for a new console when it needed, which I believe it started right after SoJ botched up Sonic X-Treme development for a last time when Yuji Naka threatened to leave the company because Stolar had picked up a copy of the Nights sourcecode at the STI request to speed up development.
His Dreamcast management was a industry set example in marketing and quality, the japanese release was weak on launch content, but the extra nine months allowed to gather all the great software released up until them for the western release, which included SoulCalibur, and by that point a flow of continuous releases as developers were finishing their projects started back in the prototype hardware days. All of his team would later get jobs at big companies, which included Peter Moore, add that the affordable price (Saturn was 100$ more expensive than PS1) and the online capabilities and you get a lightining in the bottle which made record breaking numbers at launch. According to the interview mentioned above, SoJ wanted to botch the release for a lowkey online only release in 2000.
At the end of the day, he was a great manager who tired to save a company who was stubborn until its near death bed. The lack of money or will from Sega to force life support on the western Saturn until the DC launch was the biggest trust issue factor with the public.