What if they speak Lashon Hora? What if they discuss business on Shabbos? What about people who don’t spend all day doing Torah and Mitsvos.
How about a definition the covers anyone who always refuses a job on Shabbos, and keeps some standard of kashrus (at least on a level that they can’t go out to work with goysha coworkers). Being mesiras nefesh to be Jewish seems a good factor in being “frum”, and it leaves out virtually all non-orthodox Jews.
Probably well under 20% of Jewish adults (under a million), but perhaps almost half of children (suggeting big changes are coming).