Being (Bein?)Adam LMakom is not less severe than bein adam lchaveiro.”
Sorry but it is. Yom Kippur is mechapeir for one who does teshuvah for aveiros between Man and Hashem, but even Y”K is not mechapeir on aveiros between adam l’chaveiro without the oveir getting mechilah from the person against whom he sinned. Btw, some people forget that mitzvos between man and man are ALSO bein adam l’Makom, because Hashem commands ALL the mitzvos, so if one commits an aveira like cheating someone in business, he has sinned both against his victim AND Hashem, and that’s what makes it worse. Just saying…