These claims have no canonical basis in the D&D texts I'm familiar with (eg Gygax's AD&D and the character alignment graph; the d20 SRD definitions of alignment).
On the alignment graph, for instance, nothing prevents a character being in the upper left-hand corner, and therefore both maximally lawful and maximally good.
Detect evil measures the strength of evil. Nothing suggests that a vrock can't register as much evil as mezzodaemon.
I think you're missing my main point, which is that which is worse of the three evils (or best of the three goods) is a matter largely of perspective... which
is in the sourcebooks.
Specifically, these descriptions of the evil alignments in the 3rd edition
Player's Handbook:
PHB (3e) said:
Lawful evil is the most dangerous alignment because it represents methodical, intentional, and frequently successful evil... Neutral evil is the most dangerous alignment because it represents pure evil without honor and without variation... Chaotic evil is the most dangerous alignment because it represents the destruction not only of beauty and life but of the order on which beauty and life depend.
Which matches the description offered for good alignments:
PHB (3e) said:
Lawful good is the best alignment you can be because it combines honor and compassion... Neutral good is the best alignment you can be because it means doing what is good without bias toward or against order... Chaotic good is the best alignment you can be because it combines a good heart with a free spirit.
In all six cases (as well as the other three cases for LN, N, and CN), the book deliberately leaves which is the best form of good or the worst form of evil in the eye of the beholder. Which is what I said.
But again, part of the purpose of the distinction between LE, NE, and CE is that which is worse lies in the eye of the beholder.
I said that yugoloths/daemons are
closer to being unadulterated evil, but that doesn't necessarily make them worse (from the perspective of a LG or CG character). And that matches pretty closely with the above descriptions where,
when NE is described as the most evil, it is because it is the least distracted by other motivations besides pure selfishness.
That being said, the idea that yugoloths are even more evil than demons and devils isn't actually without basis. Here's a relevant excerpt from
Planes of Conflict, a 2nd edition Planescape supplement:
Planes of Conflict: Liber Malevolentiae said:
The yugoloths are thought to be the most evil creatures in existence. Having been spawned on the Gray Waste, the plane that supposedly exemplifies the evil of the multiverse, it seems only natural to assume that they embody the wickedness of their home plane.
It's also worth noting that in the 2nd edition
Player's Handbook, alignments such as LG, CG, LE, and CE are explicitly labeled "combinations," where loyalty is divided between the interests law/chaos and good/evil. When discussing the basis of alignment, the book talks primarily in terms of law vs. chaos and good vs. evil, rather than the specific nine alignments.
A lawful good character is a good character who acts lawfully and believes order is the best way to promote good. A chaotic good character, conversely, is a good character who acts freely and believes that if people are free to do what they want everyone will be better off. A lawful evil character is a character who enjoys controlling and dominating others and who use social structures and complicated schemes to torment others. A chaotic evil character, conversely, is one who not only believes they should be able to do whatever they want but does so in such a way that actively (and purposefully) brings misery to others.
A paladin who aligns with a demon or a devil is not somehow doing a less evil thing than one who aligns with a nycadaemon.
I've already addressed this above, but it's interesting you should make this claim when you were earlier arguing that chaotic evil characters were
obviously more evil than lawful evil characters. That seems an inconsistent claim to me. At the very least, by your logic, a nycaloth should be
more evil than a pit fiend.
The meanings given by the web-page that Nivenus cites have no real basis either in the classical languages from which the words are derived, nor any standard English dictionary. See eg
this dictionary website which gives as its opening definition of "ethics" the completely orthodox "system of moral principles".
Firstly, appealing to the original meaning of either word is an "etymological fallacy." Words' meaning change over time and the fact that morals and ethics both have a fairly identical meaning in their original language doesn't actually guarantee their meaning today should be identical. Cow and beef both originally meant "cow" (in Old English and Old French respectively) but only one of them has that precise meaning today.
Secondly, I never said the words were universally held to have disparate meanings. But I've definitely seen the debate over how ethics differs from morality outside of discussions of D&D (quite frequently actually). The words are sometimes synonymous, sometimes they aren't. The Cambridge Dictionary of Philosophy notes that the word "ethics" is "commonly used interchangeably with 'morality'... and sometimes it is used more narrowly to mean the moral principles of a particular tradition, group, or individual." The truth is that, as with a lot of near-synonyms, the two terms often mean subtly different things depending on the context.
Here's another discussion of how the two terms relate to one another (and how they are often distinguished).
Thirdly, it was never my point that D&D's usage of the terms corresponded directly to these distinctions. Merely it was that the distinction between ethics and morality is not, in of itself, an innovation of the game's.