You whole argument is based on this, but I don't have the same view at all. Why do you think there can be no (even last minute) redemption or (last minute) sudden fall ? Why would some acts not count more than others, and the same for circumstances ? Why does the end not matter more than the path, or the other way around ?
Because that's how alignment is executed by the fundamental reality of the planes. Redemption cannot occur last-minute, and falls only occur last-minute if you break one of the universe's hard-coded rules that cause irrevocable fall no matter what your life was like (e.g. murdering an innocent). The game's mechanics for how alignment changes are
hard-coded into the planes themselves in the Great Wheel. Alignment isn't a weird kludge instituted by human GMs so we can talk about concrete moral consequences to actions; it is an inherent, objective, hard-coded, and
completely uncompromising ruleset of reality, such that physical objects in the planes will literally re-align themselves to make sure that they are
forced to adhere to their "actual" alignment. Hence the sloughing off of an entire layer of Arcadia into Mechanus when its residents became too obsessed with Law and had ceased to be sufficiently "Law-with-Good-characteristics."
Like, I'm not making this up out of nowhere. Alignment in the Great Wheel is the sum of your actions, coldly calculated by the universe itself. There is no judge to appeal to, and every deed and decision you make is instantaneously and inerrantly added to your "credit score," as ironically named earlier in the thread. It has both a set of "if you do these things, you are damned forever, no matter what" rules, and a "the consequences of your actions matter, not the intent of your actions nor the content of your heart." The universe doesn't
care if you save the orphans because you want a cushy afterlife or because you genuinely love children and can't stand the thought of them being hurt; it only cares
that you save orphans or don't.
Moreover, there are a lot of intermediate planes, which means that you might not even go all the way down to hell, depending on the act and the rest of the life.
My apologies. You might get sent to one of the five
nigh-identical "this is a blasted wasteland of evil" planes (which I had to look up, as I can never remember which is which: Pandaemonium, Carceri, Hades, Gehenna, and Acheron. Leaving out only the Abyss and Hell because those are famous enough to actually be remembered on their own, since those two are
also nigh-indistinguishable from the horrible awfulness of the other "lower planes." Other than having giant cubes vs giant spheres, can you tell the difference between Pandaemonium and Acheron?