They all interbred with viable offspring. They are all one species. Denisovans, Neanderthals, Homo Erecti did not go extinct. They fused with Homo Sapiens. They are among us/in us still. The percentages of DNA are low for the other varieties because at any given time there were far more Homo Sapiens than there were the others.
It’s unlikely that Homo Sapiens existed at all at the time, more likely, given the DNA evidence, that Homo Sapiens resulted from a lot of such trysts.
I have a lot of Neanderthal, according to my ex-wife.