I used a pocket WiFi from Japan Wireless at the parks in October. We had two modern Android phones (Pixel 6 Pro, Pixel 9 Pro). It all worked flawlessly in the parks and everywhere else that we traveled in Japan. We were on the Softbank network, which didn't seem to be deprioritizing us at all. The pocket WiFi device didn't support 5G connections, though.
I also tried T-Mobile roaming a few times just to see how well it worked. I had a solid connection just about everywhere, but it was slow. I'm on an older, grandfathered plan that only provides free data at 256 Kbps, though. None of that "first 5GB is high speed" stuff for me!