My recollection is that mtDNA studies showed at least no female Neanderthal ancestry for modern humans - strong evidence against this "One Species" proposal.
Shh, don't confuse them with facts.
Be careful not to get your definitions wound up in the "tow line" of Evolutionary theory. A common failing.
I am fairly certain the three professors are familiar with your objection and have chosen a more conservative approach than you two have. I tend to align with more conservative thought, where caution and disclaimers are the method of preference. Just-So stories are on the chopping block in our brave new scientific world as scientists who get untangled become emboldened.