The mishan in Mas. Yom Kippur (8:9) says that Yom Kippur is not mechapeir sins that are bein adam l'chaveiro, between a man and his friend. Therefore, it seems that our prayers for forgiveness on that day should be centered on sins between ourselves and hamakom because for those, the day is efficacious. But in the litany of sins (the al cheit) we confess and ask forgiveness for, the following sins (or sin categories) are included:
zilzul horim umorim
I can understand how one could extend any of these to include an aspect of bein adam l'makom, or how some could be offensive to hashem even though they don't somehow, rise to the level of actionable when involving another person in a certain way, but some these, especially ones about extortion or bribing seem pretty clearly about our interactions with others. If so, why are they included if Yom Kippur is not designed to be mechapeir them?
Or are there other sins which are not on this list that are purely between people so they aren't covered but somehow, the ones on this list are. Any clarification would be appreciated.