“As for the claim that no changes having been made since Sinai, this is errant nonsense.”
Of course, “changes” are made all the time. That is exactly the point. Since there are constantly changes, any kind of change doesn’t qualify Judaism as a new movement. If it did, then any kind of Judaism would be a new movement every second. The point is that it is inherent in the defintion of Chareidi or Frum that there are continuous changes, and therefore Jews have always been Chareidi or Frum (despite the type of changes being discussed) and therefore it is not a new movement.
In order to qualify as a new movement, there has to be a change that is a change from the type of changes that take place on a regular basis (that are not really changes since these changes have been taking place since Sinai, and there is no change in the type of change taking place.)