I don't have OTA tv, but I know what you're talking about.. I think at some point, Roku changed the way the volume is setup..
When I got my TCL Roku 40" tv a year and a half ago, volume 30 meant "pretty reasonably loud", but unfortunately volume 40 and 50 sounded almost exactly as loud as volume 30.
I'm guessing they made the volume settings more precise, meaning you hear a definite difference in volume, at all levels, not just the lower levels.
Yeah, I got some Rokus.
https://youtu.be/d1CSEeqWl10