To make smart YouTube tv as the default app one needs to uninstall bundled youtube using adb by:
"adb shell pm uninstall -k --user 0 com.google.android.youtube.tv"
And now when YouTube is used with Google assistant, one can set the default app.(just disabling the app from settings doesn't work)
It works like a charm. Hope it helps to everyone out there.
Just wondering why does everyone use it over the stock app? I've only ever used it on my old FireTV stick because there wasn't an official app available. What exactly are it's advantages?
In my experience the resolution selection felt a bit hacky and the cast support didn't always work, but apart from that I didn't really notice any differences.