Yes different characters with different moral characters and their own moral success and failures can end up being described with a similar summary when describing just the high level position on the spectrum.
The Opening post is also suggesting having Detect ___ spells look one level below the high level summary. So the person that lived a mostly amoral life might not ping either Detect spell but someone with a similar high level summary that had a life full of moral consequence might ping both Detect spells.
That is stretching my metaphor* by assuming the alignment relevant intents/actions/consequences of a character must be quantified and treated as vectors. I would hold you are making it harder than it needs to be.
*The x coordinate from a sum of vectors is similar to summarizing a character's moral character to a position on a continuum. Both methods, despite their differences, summarize the overall position but, despite not showing the original information, it doesn't delete the additional information. Just like the sets {+220, -190}, {+25, -15, +25, -15, +25, -15, +25}, and {+30} are different despite sharing the same sum (30).
This idea of merging the detect spells, combined with them being somewhat more detailed, is interesting. I suggest simplifying it to:
A) Detect the qualitative (not quantitative) strength of each alignment. You might detect someone with a faint Order aura, moderate Good aura, strong Chaos aura, and no detectable Evil aura.
B) After more time studying the auras you might detect the Order aura is from a low number of infrequent but high impact events but the Chaos aura is from a deluge of behavior. They probably have a few rules that rarely come up but they would never break. Given the milder moral auras, the caster might conclude these rare rules might or might not be related to a moral code.
Thank you for giving contrasting examples of high level summaries.
Sidenote: I mentioned above that I did not state they did cancel out. I stated a summary does not share the whole story, but neither does it delete the whole story. This is true in my (unstated) system, and the 2 you mention. /Sidenote
Summary of what I was saying: Many that use descriptive alignment already use alignment continuums because it is easy to recognize the high level summary is not the full picture. Hmm, the OP has an interesting idea of letting Detect/Know Alignment spell see one level deeper.
In reply to you concern, I agree that letting the Detect/Know Alignment spell see one level deeper takes little effort if one is already using descriptive alignment. You are already describing the character's alignment based on what the character's characterization was/is. Letting the spells see your penultimate conclusions is not much more work than letting them see your conclusion.
Edit: Where did all the "Â"s come from? I did not edit the quotes. That is weird.