Dear Avram,
Beliefs do matter -I think we agree on this part, that strength of faith and piety, is a very strong determination of one’s religiosity. I’m using the ‘beliefs are irrelevant’ line, for the opposite extreme. When determining what is within the ‘norms’ of Frum Yidden, I think it is about observance. As beliefs alone does not make a Yid. So long as all the practice is being practiced, there is room for more extreme thought systems. Although these systems may eventually convince them to stop practicing, the ideas themselves to not put them outside the ‘norms’. (And I would preemptively note, that observance is very strong in Chabad. Particularly, Chabad Yeshivos.) For example; davening to the Rebbe keeps being mentioned. Whatever it is or isn’t, they have not changed the standard liturgy. They still daven the same tefillos as the rest of us. Whereas Conservative, as well as some far left Orthodox, have reimagined the service to reflect their innovations.