That's why you don't use newer features until they're absorbed by the standard.
Well, OK, so when should I expect that I can build a brochure site for a hotel that uses HTML5 videos and have one video format and one set of custom controls to work with? Because the world has moved on and Flash is no longer a viable option for this kind of work despite offering those advantages for many years, thanks to much the same browser developers who can't get their act together and actually provide a better replacement. They can't even manage to make the default "this is a video" overlay look the same, or even put it in roughly the same place so you can design placeholder graphics accordingly.
If your company's video site actually is YouTube then this kind of problem probably doesn't affect you all that much. However, for normal web sites that are just trying to take advantage of multimedia as part of the presentation, HTML5 audio and video are a bad joke, and the punchline is that all the much better technologies that used to be viable alternatives have been deliberately killed off anyway.
You may not care for the practice, but nothing leaves my hands into production until it validates
But this brings us back to the original question from my first post in this thread: why? What objective advantage do you or your employer/client gain by insisting on such compliance?
I do sympathise with your position, in that it should be an advantage to follow standards, and browser compatibility now and in the future should be practically guaranteed by doing so. The world would be a better place if this were the reality. But it isn't, and so pragmatically, I'd rather build web sites and apps that work than sites and apps that dogmatically tick the right boxes even though it requires more effort and offers no demonstrable benefit.