As I have been talking with people about Wifi on trains, Wifi in public spaces, etc. in Japan.
So to sum up Wifi in Japan:
public transport mostly no
Shinkansen available but the speed...
public/touristy spots often available but speed...
Bars/restaurants mostly no
Museums Yes & mostly good
Hotels Yes & mostly good
Would I travel without a E-SIM/SIM just relying on free Wifi?! - No.
The attached picture shows the best speedtest result in a Nozomi Shinkansen...







