OTA TV Tuners fill this niche.
It's been a bit since I've done this (I'm not watching live TV anymore), but something like HDHomeRun worked fine.
It basically pairs an antenna with a small computer to convert to network traffic, then gives you an app on your streaming device to play it back.
You do need to be able to run the vendor's app, and you'll get stuck with that UI for live tv (So yeah - totally agree that you're compromising the UX). But still no reliance on the "smarts" built into the tv.
I have an HDHomeRun box and use it through Plex. I've never installed the HDHomeRun software. Plex immediately recognized it as soon as I plugged it in. There is a noticeable amount of latency between selecting a channel and starting the stream, so channel surfing is pretty cumbersome, but I almost never do that. With the paid version of Plex (Plex Pass), you also get DVR support which automatically removes commercials from the recording, so that's pretty much the only way I use it.