Driving a v8 sports car that can do 200mph on your average commute to work, on city roads with a limit of 35mph...people still do it.
Point is, for me, dedicated appliance, means rock solid reliability. That is what is does and only that. I am not one to have my main router also be a NAS, or media server, or AIO type device, a dedicated router does the one thing it is designed to do, route, and it does it at peak performance and efficiency.
(I use a ER-12)
I also, do not subscribe to having all your eggs in one basket. If one device does all the work, it goes down, everything goes down. Segregated setup, to me, makes most sense.
A tv DVR, could be recording something, or in use when i want to maintenance or tweak my other always on devices, or need to reboot. It as well as my stand alone DNS server, are each running on a Pi, and are the 2 main things that are rarely touched or rebooted.
Also, since they use only a few watts, can run for several hours easy on a average UPS.
(sure, those other mini pc's like NUC or this rando china one, only may use 10 to 15 watts, but, that is double or more than the Pi still, and thus, cuts the battery power run time in half or more, not to mention, the cost to operate per year is double as well)
Also, i first started out with Channels DVR running on a Intel NUC i5 5th gen system, running Linux Mint. When i switched to the Pi, i noticed the experience was noticeable zippier and more fluid. Loading the web admin even was faster. A few other users, at the time, also posted they had the same experience. Comskip processing was marginally slower, but the over all stability and smoothness was noticeable. I have not rebooted or powered off the Pi channels is running on in over a year, save for the occasional os image update they push out.
Edit: Also, dedicated appliance is best, as there is no other network traffic or process to interfere or slow down the DVR. If i ran CHDVR on say my Windows NAS system, which i routinely transfer large files to and from, or have multi day long uploads going(Backblaze backup), that saturates the NIC interface.(also runs Plex).
HDHR streams are very sensitive to any disturbance, and if recording or streaming, the NIC has to pause packets or re-send, cause of oversaturation, you get corrupted data or delayed data, resulting in video breakups or artifacts etc.
Also, if one maxes out the CPU, say encoding video with Handbrake, on the server system, it cripples any other program needed cpu. (I had these issues when using the NUC as my server and also used it for many other tasks, though, it was only a 2c/4t cpu)