>It comes down to the acceptance of those postulates. However, they
can't really be accepted (see Yitzhak's response). So, you can't
really build a plausible theory on unacceptable assumptions.
What do you find unacceptable about the postulate that
tri-consonantal roots were derived from bi-consontantal roots, and
what is the alternative? That the former were derived full-blown ex
nihilo, like Athena from the head of Zeus?
And although the postulate that Tet was a reflex of Tav may not be
acceptable, the postulate that Tet and Tav were often confused within
and between languages should be acceptable?
However, even if the latter postulate isn't acceptable, the identity
Pe-Tet/open = Pe-Tav/open is still, imo, sufficient grounds for
believing that the roots are variants.