Quicktime on Mac OS remains a shitshow to this day. I still have not figured out how to use third party srt files for subtitles.
There is support for hardware accelerated h.264 decoding in VLC; you just need to enable it. I think the option is in Input and Codecs tab in the preferences.
The video and audio streams within such files are, by design, out of sync, and requires playback within QuickTime to actually get the file to play back properly, as the content creator intended. Workarounds exist, and some playback software can handle the problem internally, but VLC in particular is not always able to.