Less, actually set prayers and shuls began after the destruction of the First Temple (Hoshea 14:3). Archaeologists have found the remains of shuls from the Second Temple period.
As for the claim that no changes having been made since Sinai, this is errant nonsense. We just celebrated a change (Chanuka) and iy”h we will celebrate another one in Adar. Minhagim are all changes. Kabbalat Shabbat, for example, was instituted by the Chochmei Tzefat (which is why Ashkenazim say it from the bima – to stress that it is not part of Arvit).