That's my experience too. I transcode a lot of video for a personal project and hardware acceleration isn't much faster. I figure that's because on CPU I can max out my 12 cores.
The file size is also problematic I've had hardware encodes twice as large as the same video encoded with CPU.
I would SO love it ! I regularly take a look at the existing offerings, and there's a few options for "transcode video as API". However it's pretty costly, i regularly have batches of videos that would set me back 30 to 80 bucks if i were to transcode them in the cloud. I don't think it can be done at any price point i'd be happy with for this kind of personal project - especially considering that the alternative is just to max out my CPU for a day or two.
The file size is also problematic I've had hardware encodes twice as large as the same video encoded with CPU.