Then you are not yet understanding me.
That some act is right or wrong for creatures of a certain nature does not make that moral evaluation subjective or contingent - the rightness or wrongness of said act for creatures of that nature is still an objective (not constituted by merely subjective features) necessary (could not have been otherwise) moral fact.
And you haven’t demonstrated that what I think is incoherent, or even unreasonable. Again, here’s it stripped down to the bare minimum:
I’ve spent some time defending the moral argument in this thread and pointed to writings where I’ve defended it further. I’m not going to bother laying out the cosmological argument here - but I have written about it on my blog, and you can probably find posts by me here on PS where I’ve defended it in the past. The move linking them is a completely natural appeal to Occam’s razor; it’s not an arbitrary choice. So your objection that I haven’t overcome Euthyphro with the usual “objective moral standard = God’s character/nature” move because such a move is “arbitrary” is, from my perspective, ultimately baseless.