I understand that there are detractors who want to remain locked in the bittersweet and not see Ennis 'move on' - as is said... Grow is a better term because many of us move on... but continue in the wasteland of our own inner bankruptcy (thinking of T.S. Elliot and Wasteland with it's "hollow men"). I wonder about those people... if they are in that same type of wasteland and either can't see or don't want to acknowledge, that there might be more than "measuring your life out in coffee spoons" (The Love Song of J. Alfred Prufrock - T. S. Elliot).
My point in this is that, consistent with canon here... in LS we see Ennis, because of Jack's death - a backhanded gift indeed, begin or restart the journey of finding his own soul... and in the process, along the way... finding the love and resources necessary for himself... ~and~ a channel for the considerable resources that he has as an individual - commitment, loyalty, strength and power - to pour forth.
If people want to remain in the bittersweet... then well and fine... but experience seems to teach... that bitter always overwhelms the sweet... and that an unwholesome attachment to bittersweet always leads to galling disappointment, disillusionment and despair...
Your whole post would take several response posts to address, and I'm just replying to this part of it at present --
You're correct that Ennis' experience with Jack is not enough to overcome the psychic abuse inflicted by him on his father, and reinforced by society's tacit approval. And after the loss, Ennis spending a certain length of time in the wilderness coming to terms with that is necessary which is why, IMO, his living alone in a spasely-furnished trailer is not necessarily a negative thing unless he never gets any further than that. Many people in RL do not, and the result is certainly, as you say, the bitter overwhelming the sweet.
If that's the result in RL, staying in the wilderness and in grief only, it might at least partially explain some of the hostility to stories like LS. In other words, Ennis spending the next decade, or two, three, four decades, in a blighted life might be seen as a validation: "
see, this iconic character can't move beyond loss, despair and psychic imprisonment; I can't either." And this is very understandable, but something being understandable doesn't automatically give it any positive power. And in the case of Ennis as a character, his father triumphing over Jack certainly does not honor the relationship. "Ennis and Jack forever" is certainly valid as far as the love enduring is concerned; "Ennis and Jack forever with Ennis remaining alone and in despair" does not.
One of the most essential ingredients for Ennis to overcome the father's evil legacy is to have not only a new love but to be in a supportive environment, something to counteract both the homophobia of the outer world and his inner fears. In LS, that translates to not only Ellery but to Wes, Edna, etc. and even to the two daughters, as exasperating as they can be in some chapters.