An individual isn't going to go ask a cleric for their credit score.
They...don't need to? I don't see the relevance.
Having a plane aligned to LG as an actual cosmic force, doesn't force individuals choices.
Certainly. Having that plane innately vacuum up all souls that die while being Lawful Good (but not Good-with-Lawful-Characteristics nor Lawful-with-Good-Characteristics, which each send you somewhere else) does.
Because it doesn't matter what you intend. It doesn't matter how you feel or what you think of others, nor whether you are truly a good/evil/whatever person, nor even whether you had a change of heart in some cases. Do too many pure evil acts and you're bound for an evil plane no matter what. Doesn't matter if you work your butt off to do better and genuinely turn over a new leaf, if you murdered even one person in a fit of pique at 18 and lived like a saint to try to make up for it, you still go to Hell.
We get a combination of:
these things being inherent cosmological facets (as in, reality itself will adjust to
enforce that Arcadia is Lawful-with-Good-Characteristics, even if that means cleaving off a chunk of the plane and depositing it in the Lawful Neutral plane),
them automatically and inerrantly picking up
every petitioner "meant" to be there, and
the very definition of "meant" to be there being so thoroughly broken and awful (because D&D alignment is HORRIFICALLY AWFUL as a moral philosophy, a "worst of all worlds" blend of all three main ethical theories)
Collectively, these mean that it is very easy to figure out exactly where you are going just from a description of the planes so long as you are honest with yourself, even if you don't actually believe a single word of what that plane's alignment espouses. Further, unless you have committed any of the unforgivable acts (which ensure you go to an Evil afterlife no matter what, so you might as well be pure evil and take advantage of the benefits while alive), you can always change which one you go to simply by doing enough showy and dramatic actions in accordance with your preferred destination. Again, no need to get your alignment credit score, just do Lawful things and scorn both selfishness and mercy for long enough and you'll definitely get into Mechanus (though why you would WANT to is beyond me). Make sure to break some minor law every day but never in a harmful or unpleasant way and you will almost guaranteed land in Ysgard or Arboria (so long as, as noted, you haven't previously committed enough evil acts to be permanently unforgivable by reality itself).
That's what I mean by alignment
determinism. It isn't just that the planes exist. It's that they are absolutely flawless in enforcing the alignment system in all its horrific glory, which does not care one whit what you believe or whether you actually exhibit virtuous or vicious qualities, it only cares whether you've broken any of its inherent rules and whether the consequences of your actions conform to the letter (not the spirit) of a given plane's alignment.
Reality itself is a vast and terrible sorting hat, and the seventeen not!Hogwarts "houses" are just as terribly written as the ones in the HP books, except these are the destination for your eternal soul, and there's no one to argue with; there will be one and only one answer for your soul and that answer is eternal. It's incredibly awful.
