Toi.
I was wondering how much the OP thought should be lost for a minhag.
For a mitzvas Asei deoraisa(!) the MOST a person has to lose is a chomesh (1/5).
If youre not equating (and you shoudnt since shabbos and sefira arent similar) why mention irrelevant examples
Poskim HAVE decided R’ Moshe allows shaving for parnassa in two tshuvas one in O”CH 4 other in the O”Ch in chelek tes (which I assume is 5)