At what point in our history did the guidance of our gedolim into something completely different, i.e. a priori dictation to all of day to day decision making
Who says it did? Perhaps for the Hamon Am who are unable to work their own way towards a derech Hashem, similar (as you point out) to the Chassidishe Rebbes who were able to be Madrich the simple Am Haratzim by having them follow the Rebbe (of course, those who were able still benefited from the Rebbe, but without blind obedience).
I believe you give too much credence to the “Internet Charaidi” (e.g. Joseph/Frumteens), without being aware that even in EY, (I would think) most Charaidim (non-Chassidim) do not blindly follow their Gedolim (they may follow due to finding out that is their Derech, or L’hepech societal pressure, etc., but not M’Kol V’Kol). A pashut example of this is Rav Chaim, about whom the Steipler was upset since he didn’t follow the Steipler’s Derech in Limud. None the less, Rav Chaim knew what was best for himself and became Rav Chaim.
I believe if you would ask Rav Chaim or Rav Aharon Leib Shlita, or Rav Elyashiv ZTL, they would say the same thing. The “Hamon Am” may be best to just be followers, but those who are capable should follow their own derech.