Absolutely NOT true. DLNA does support SRT subtitle files. Its just, as was explained previously, your Samsung Smart TV DLNA client does not (from streaming network content). We covered this in your previous thread and provided one potential solution to get around the issue that include burning in (hard coding) the subtitles into the video file.
Not sure why the quality would get worse. I’ve used Handbrake to hard code/embed/burn in subtitles from SRT files to MP4 video files and didn’t notice any change in the video quality.
Is the suggested workaround the ONLY option? No. You can pester Samsung to see if they’ll fix their DLNA client to work with certain NAS devices like the My Cloud where their TV’s are having trouble streaming media. You can use a third party device like; a Raspberry pi loaded with Kodi, Amazon Fire TV loaded with Kodi, or a Roku all of which should support playing SRT files from the Twonky Media Server embedded in the My Cloud to your Samsung TV. You can load the video file + SRT file onto a USB drive and plug that into your Samsung TV. Or simply use the method above to burn in/embed the subtitles which isn’t necessarily the best workaround to your problem, but is a workaround.
Based on the number of complaints specific to Samsung TV’s both here on this support forum and in a general internet search, there is obviously something wrong with the DLNA client used on certain Samsung TV’s when used to access content on a variety manufacturer’s NAS drives.