I don't know which historians you're reading, and what their agendas are, but not all of these criticisms are invalid or anti-humanist. That historians can no longer agree on the precise date the Renaissance began is more the recognition that the impulses that led to the Renaissance (the revival of antique forms and subject matter) actually existed much ealier than supposed, and in the works of artists (like Nicolo Pisano) who were once considered Gothic. In fact, historical consensus now seems to consider that the classical tradition was felt through most of the so-called 'Dark Ages', and that Christian artists borrowed freely from Greco-Roman images and transformed them into the vernacular of their own Gothic art.

The belief that the 'Dark Ages' weren't quite so dark as Vasari might have liked to imply, and that the Renaissance wasn't a complete tabula rasa but retained elements of the Gothic, isn't a rejection of what the Renaissance stood for.