You eloquently express my take on acceptance, that started with this passage from the famous page 417 of the "Big Book" of AA:

"And acceptance is the answer to all my problems today. When I am disturbed, it is because I find some person, place, thing, or situation — some fact of my life — unacceptable to me, and I can find no serenity until I accept that person, place, thing, or situation as being exactly the way it is supposed to be at this moment. Nothing, absolutely nothing, happens in [the universe] by mistake. …unless I accept life on life’s terms, I cannot be happy. I need to concentrate not so much on what needs to be changed in the world as on what needs to be changed in me and my attitudes."

I have always interpreted that to mean acceptance in the moment, and from moment to moment, but that one does not have to accept the unacceptable as permanent. In that way, one feels serenity rather than resignation in the face of the "unacceptable."

If you or your readers want to read more of my thoughts on this, and my thoughts on "life on life's terms," here's a link to one of my essays: https://medium.com/my-selection/my-selection-alcoholics-anonymous-colloquially-known-as-the-big-book-638b5ad7f2e1