Value is one dimension of colour so, value > colourfulness
, although that sounds a bit awkward. So: value is more important than hue or chroma; yes, that's much better
If you take the value information only from an image you're left with something that still reads quite well in most cases (as B&W photography shows us).
If you take the value information out
of an image on the other hand you can be left with something that's impossible to interpret; at best it's just very flat and odd-looking - who wants to make an image where shadows aren't darker?