As far as I'm concerned an HTPC is by far the best device for streaming. It s flexible and you have pretty much instant access to anything out there.
I do not use a TV as the source ever on any of my systems, and would never consider doing so. I have no time for ROKU, Firetsticks or any of those devices. The only streaming device I do use sometimes is Chromecast which is brilliant. That is mainly used on my vintage rig, that has no receiver, just an HDMI auto switcher.
Receivers, pre pros and TVs are not the units to do streaming from.
What is required is a high quality unit ahead of a pre pro or good receiver.
Couple of points.
I do agree that using a TV as the main source is not ideal. I myself have a Sony TV with Android TV built in. It's great aside from the audio issues that have already been covered.
I too used to use ONLY an HTPC, but 4k and HDR have thrown a wrench into that. HTPCs are not capable of properly playing back this content seamlessly. It's a huge pain to get it to work properly.
I've got an Nvidia Shield TV box that will play back anything. It's as close to a perfect device as I've been able to find. I use enough streaming services that maintaining an HTPC to work the same way is all but impossible.
I never would have thought something could replace my HTPCs, but it has happened.
Once I get my theater up and going a Shield TV will be the only source.