A fifth of the entirety of humanity is a heck of a lot. If you want to claim that Denisovan or Neanderthal ancestry is just as crucial as the basal homo sapiens, you are writing off a good chunk of humanity. Combine this with the purging of Neanderthal DNA (and the likely purging of the little bit of Denisovan introgression), it's clear that one of these things is not like the others. Let's not overstate the implications of these things.