The advantage of subtitles over voiceover is that someone learning the language can compare the two. They also prefer to have Welsh and English side by side in marketing leaflets and things of that nature, for the sake of comparison. TBH as a monoglot I don't find that easy to scan on a bilingual page.
MB was referring to the "welsh not" the practice of putting a board around the neck of a school child who spoke Welsh. Sadly this is one of the main reasons Welsh declined so severely, so the language is still recovering. To say it's not relevant is ignoring the fact that its impact is still very real today.
I don't speak Welsh and probably will never learn but it would be madness not to have a Welsh media, and to acknowledge that in some jobs you do have to be bilingual to do them. As ever you have to judge on a case by case scenario and having worked in a bilingual, state sponsored, organisation for many years, there are very few examples I can point to which were wrong in an every day way.