The argument is reductionist and similar to standard model quantum theory: below a certain scale things behave very differently. Then a conclusion from that: there are no medium sized things at all.
Except that the QT goes very differently from reductionist biology, because of the mysterious contradictoriness of quantum phenomena such as coherence and entanglement. Things can be moving and still simultaneously, in two different places at once, and so on.
I would prefer to say that there are no species for the opposite reason. Not because species is only a human (or subjective or whatever) imposition on the hard data. But because a lion is always a not-lion at the same time.
But this line of reasoning does resemble parts of mine! Happy to read it!