What I'm having difficulty reconciling is the following statements of
yours:

"If you can receive the G/S prior to the PFAF, it's only advisory in
any
case, so you are free to use it as you choose, provided you don't
violate any minimum segment altitude or stepdown fixes or any aspect of
an ATC clearance."

I totally agree.

"The new CFI is technically correct but the old CFI is far more
practical."
"In the case cited, the CFI is nitpicking but is nonetheless legally
correct."
"I agree that the CFI is procedurally wrong, although legally correct."


So how can you assert these, *given that in this instance* it is
physically and logically impossible to "violate any minimum segment
altitude or stepdown fixes or any aspect of
an ATC clearance", because
a) the ATC clearance was to maintain 2000 until intercepting the
localizer, and
b) the procedure was to descend on the glide slope to the minimum
segment altitude (1800) at which point the G/S becomes primary.

The point is that blindly following the glideslope has the potential
at places *other than SCK* of causing violations of published
altitudes. Following the G/S is not a violation per se, busting
published or ATC assigned altitudes is.
The CFI is not "technically correct" or "legally correct". What he
could have said, after the flight, is that if one chooses to follow the
G/S prior to the PFAF one needs to be mindful that published and ATC
assigned altitudes have to be complied with, but that at SCK that was
not an issue.