In the 16 days I was there, every single place which accepted my Suica card also accepted Visa and Mastercard. Amex was also more widely accepted than I'd have thought. And this was 5 years ago before Covid forced even more contactless transactions.
The conversion rate you get when you buy forex in cash will no doubt mostly be worse than that offered at the time of transaction by a modern travel card/credit card which doesn't charge fees such as Revolut, Monzo, Halifax Clarity etc. How do you think places which exchange foreign currency in cash make any money?
I don't need to argue against anyone. I've been and experienced not having to use cash half as often as websites like that implied, and so have several others in this thread. Especially since Covid, the notion of Japan being a cash based society is out of date for all but the most rural areas but even then you're never too far away from a combini.
Taking some cash is a good idea of course, but you don't need to take your entire planned spending money.
If you're going to look for government advice on this topic, I'd take the Japanese themselves over ours!
https://www.japan.travel/en/plan/credit-cards/