What I'm interested in is, do you believe in literal post-mortem rebirth? I'm not expecting you to accept it, just trying to understand the stance you have taken on this matter. I suspect it is not a big part of why you practice (I maybe wrong). I am reminded that the Buddha's udana at the point of liberation was all about stopping samsara.
"Why is that? From an inconstruable beginning comes transmigration. A beginning point is not evident, though beings hindered by ignorance and fettered by craving are transmigrating & wandering on. Long have you thus experienced stress, experienced pain, experienced loss, swelling the cemeteries — enough to become disenchanted with all fabricated things, enough to become dispassionate, enough to be released."
— SN 15.3
Note how the Buddha deftly switches between the mundane endless (no place in ultimate truth talk) transmigration, and says that this will make you dispassionate about fabrications (ultimate truth, here and now). By seeing and understanding what is in front of our eyes, we become able to overcome the past and the future, metaphorically speaking.
[The Buddha:] "Don't say that, Ananda. Don't say that. Deep is this dependent co-arising, and deep its appearance. It's because of not understanding and not penetrating this Dhamma that this generation is like a tangled skein, a knotted ball of string, like matted rushes and reeds, and does not go beyond transmigration, beyond the planes of deprivation, woe, and bad destinations.
Now, if he were so concerned about literal rebirth, he would include it in the DO- as it is road map; it's not seeing, the cause for transmigration. As you correctly pointed out, if all that mattered was what is happening in the present moment (ie if it were 'therapy'), then avijja paccaya sankhara is all that is required to be stated. But this is far more than that. We are required to have faith in the Buddha, dhamma and sangha and accept that not everything can be known directly, to everyone (such as rebirth and kamma). But that doesn't mean they are not relevant. One could state that it is possible to do without them, and that would be true, especially if you are prepared to leave out those teaching from the suttas (which you could do), but better to be consciyosly aware of that fact, rather than saying that those teachings are corruptions and that you hold the entire teaching within your view (and that others are wrong- which I see you are not doing).
I might tbrow this in- If all there was, was the removal of the three poisons, and after that there was life (becoming), minus the suffering it wouldn't be much of a proxy for the ending of rebirth - who knows, you might have just suppressed lobha, dosa, moha. But if you experienced the suffering of arising and passing away, and then saw the non-arising of fabricated phenomena once you got rid of avijja, even momentarily, you would have some reassurance that this path can stop the suffering of arising and passing away AND any form of rebecoming. It is not absolute proof, but is as good as it gets, IMHO. The rest of it takes sadda, the type that cannot be replaced with panna (quite possibly the reason why it is a faculty in it's own right).
Ps- as to the utility of a mixed (mundane/conventional/ultimate/internal/external) DO, as I believe in rebirth, (as per mundane right view) and Siddharta Gotama's initial problem was old age, disease and death (not the impermanence of fabrications), so it makes perefect sense that the epitome of Buddhist teaching should contain answers to those very exalted questions, lest it be rather unsatisfactory (mind the pun) and rather bland, threadbare fare, for those poor in view. Not only does it contain answers to that but it contains the solution to 1) overcoming becoming, which happens in a future life, in this life 2) the answer to the eradication of suffering through the eradication of craving 3) the eradication of sankhara dukkha, by the erradication of avijja 4) a explanation anyone at any level of practice can appreciate (Buddha asked his disciples to at least take it on.. faith, in one sutta). 5) is a summary containing within it many threads, but has enough for disciples to practice from various angles, according to their predispositions 6) shows exactly how the cards are stacked and exactly how the cards fall as well- it is pure genius!