Stative Verbs, or Perfect Tense

In reading Andrew Sihler's "New Comparative Grammar of Greek and
Latin", I noticed that he makes a special effort to point out that
what traditional grammars denote as the "perfect tense" in PIE was
not a tense and did not denote completed action, but rather was a
class of verbs (verb "type", in his phraseology) that denoted a state
or condition, which was tenseless and voiceless. He says that this
traditional view is outdated, wrong, and rejected by current opinion.
What I want to know is, how certain are linguists generally that this
is the case? Isn't it the case that in all the attested IE languages
the descendant of the IE stative (as Sihler calls it) is actually a
past tense, whether indicating completed action or simple past time?
And some verbs that denote a state or condition
(i.e. "sit", "lie", "be") Sihler says did not have stative forms.
Does this suggest that what he terms "stative" endings perhaps were
not primarily used to indicate a state or condition?
Sihler says that stative verbs cannot have tenses. But surely the
notions he says are conveyed by the stative, such
as "knows", "has", "is dead", can have a past tense,
i.e. "knew", "had", "was dead (in narration)"?
Sihler also repudiates the traditional idea that the perfect's
meaning was to express a present state resulting from previous action
or experience. But I see no reason to reject the traditional idea
that "knows" can be derived from "has seen", "has" can be derived
from "has taken", or "is dead" can be derived from "has died". To be
sure, Sihler offers some examples of IE statives that he says cannot
be so analyzed, e.g. "dares", "hates", "yearns for", "owns/has",
and "prevails". To this I say "owns/has" = "has taken, has
gotten", "prevails" = "has won", and of the others, the IE root
for "hates", *od-, may be rather a root *H3ed- without original o-
grade, while I do not know what root he has in mind for the
meaning "yearns for".
Thus to summarize, I am not so convinced that the traditional idea of
the stative as a perfect tense is wrong. Would anyone care to
comment on this, and perhaps offer an explanation as to why the
traditional idea of the "perfect" has been so thoroughly rejected? I
just don't buy Sihler's hypothesis, I still find the traditional idea
more believable.

Regards,

Andrew Jarrette