Listen, before deviating more from our own original statements, let’s restate our opinion and our understanding of each other’s:
You say, Bein Adam Lachaveiro Mitzvos are commanded to us because of the benefit they have to your friend or to society. You also agree that since Hashem wants us to do this, it is therefore a Bein Adam Lamakom. You also seem to add some mystical merit in it all.
I say, all that applies to behavior that is not mentioned in the Torah. What is in the Torah explicitly, is not merely a nice behavior. You don’t get Malkos for making fun of your friend but you do get Malkos for charging Ribbis. The purpose of Middos Tovos, too, is to be wholesome people that are able to be a dwelling for the Sh’china.
When we say, Derech Eretz Kadma Latorah, that is because it is preparing the person to be able to go to the next step. Derech Eretz Kadma Latorah is not talking about Mitzvos that are in the Torah, explicitly. These are real Mitzvos.