I’m afraid when it comes to Linux TVH v NPVR is a no contest. TVH wins hands down. . Net Core is clunky and is closed source and while you state that you are somehow privy to the developers API that is not a consideration in TVH. Everyone is free to develop it in any way they see fit.
No I don't have access to the API. What I said is I have requested changes to the API functions I use with pvr.nextpvr and the author has always been responsive to change. The author is also quite willing to make changes to the application modules itself and as you noted new versions are frequent. We are testing on 6.1.4 right now. Closed source doesn't mean that the code is not dynamic.
I am not here to discuss the distinctions and personal biases between open source vs closed source, Linux vs Windows vs macOS, or managed code vs unmanaged code. The author certainly address any limitations in the code if proper support is followed and that is what is import to me and most users, although maybe Windows users are more open to discussion then some Linux users.