Same thing with mustard. Mustard used to be spicy, then "yellow mustard" came out, then yellow mustard became mustard, then actual mustard became "spicy mustard".
what you refer to as "yellow mustard" or just plain "mustard" australia at the very least labels as "american mustard", and then label the "spicy mustard" as "english mustard"
If you buy mustard seed there is often yellow and red seeds. Use yellow variety plus turmeric and vinegar for your standard American mustard. Use red and vinegar and beer/wine for your brown mustards. In my experience there is little difference in heat, what matters is time to mellow. The older the mustard the less spicy horseradish/wasabi sensation. Perhaps it’s oxidation.