ROB
I have no idea how you understood the Rambam.
The Rambam states quite clearly that he is discussint the three general approaches taken towards Mamorei Chazal. No where does he state in any way that he is only talking about specific cases. Not only that but if he would be discussing specific cases I would think he would mention which ones.
Secondly he states clearly that the problem is that these people feel they know more then Chazal.
A
I have no idea how you can possibly come out of this Rambam that it is possible to “question the paremeters” of Chazal when the Rambam is takes great pains to state exactly the opposite.
Furthermore this Rambam is discussed by other’s (the Shelah comes to mind) and no one ever understands it the way you are stating.
As for Slifkin himself, I have read one of his books and afterwords went on his website to confirm his beliefs.
Another core principle of his belief is actual having a “rational” approach, he rejects mysticism, so I have no idea how you can infer this Ramabam as agreeing with his approach, he states quite clearly that in his view Chazal got their knowledge from Pliny afact the Rambam clearly disputes.
And I would add that I have studied these matters and I can pretty confidently state that there is virtually no source that adopts the approach he takes.
An example being would be that he is correct that RSRH does take one aspect of the the view he advocates in a famous letter regarding Aggadita, however the conclusions he takes of of that in his approach towards Mitzvos (what he considers the Rambams approach) is one that RSRH bitterly attacks and belittles in The Nineteen Letters, Letter 18, RSRH writes regarding it that it did more damage to Klal yisroel then Moses Mendelsohn’s teachings!
So in other words Slifkin uses one letter where RSRH endorses one aspect of his views to imply that RSRH is a traditional source” that endorses his philosophy, when in fact RSRH wrote so strongly against it that when the Nineteen Letters was originally translated into Hebrew, the Chazon Ish himself advised the publishers to leave it out for fear that RSRH would be taken out of context in attacking the Rambam in general instead of one understanding of the Moreh Nevuchim specifically.
And the vast majority of the sources that Slifkin qoutes do the exact same thing.
There is virtually no one who endorses his approach or his conclusions. It has been used by Hellenists, By Maskilim, and by the founders of Conservative’s and at every time that it has reared it’s head it has been bitterly and vociferously denounced.