First, the quality of output of hardware accelerated transcoding is in most instances noticeably worse than CPU transcoding, as in most people can discern the difference watching two videos side-by-side.
Second, CPU transcoding is more than enough to keep up with most streams. For instance, 1920x1080 h.264 streams can be done in real time by even a modest 4 core processor. People who want 4K h.265 can buy a fancier CPU.
Third, most people are served perfectly fine by pre-transcoded files. Your comment about subtitles isn't correct - most streaming devices can accept subtitle metadata, and even if subtitles need to be burned in, they can be burned in to a static file and/or generated in real time by a CPU.
What's interesting is that the same people who want Intel Quicksync claim they want to transcode to the best quality that a device can support, then say they don't want to transcode to a static file because they don't want to transcode to a lower resolution / bitrate than what their best device can support, but want to be able to view things at the highest quality wherever they want. They've been tricked, because if they really cared about quality, they'd care about the difference in quality between QuickSync and CPU encoding.
That's why I tell people that if the really want highest quality real time transcoding and have sources that are ultra high quality, they'd be much happier with a Ryzen 7900 than with Intel QuickSync. Side-by-side comparisons would bear this out every time.