This has been my experience as well. Last year I went on a trip through Morocco and the UK. Never worried about my usage despite using services like Spotify and Google Maps. Got a bill that I would expect with traveling within the States.

My normal day-to-day has me on WiFi the majority of the time so my phone bill usually comes out to about $36 a month.

Edit: For the curious, I've been using Fi with a Pixel 2 since the phone was released.