I'm certainly not defending 2e! But it feels like it was a darn sight better than 1e in this regard.
Here we disagree. I think Gygax's PHB and DMG are more coherent than 2nd ed AD&D. As I posted upthread, they identify a contest between law and chaos as to the best means to achieve good. (And as I also noted,
good is taken to be something we're already able to identify. Gygax's alignment system assumes this; it doesn't inform us about what
good is.)
The paladin in the original PHB is also quite coherent, in my view (pp 22, 24):
Law and good deeds are the meat and drink of paladins. If they ever knowingly perform an act which is chaotic in nature, they must seek a high level (7th or above) cleric of lawful good alignment, confess their sin, and do penance as prescribed by the cleric. If a paladin should ever knowingly and willingly perform on evil act, he or she loses the status of paladinhood immediately and irrevocably All benefits are then lost, and no deed or magic can restore the character to paladinhood; he or she is everafter a fighter. . . .
An immediate tithe (10%) of all income - be it treasure, wages, or whatever - must be given to whatever charitable religious institution (not a clerical player character) of lawful good alignment the paladin selects.
Paladins will have henchmen of lawful good alignment and none other; they will associate only with characters and creatures of good alignment; paladins can join a company of adventurers which contains non-evil neutrals only on a single expedition basis, and only if some end which will further the cause of lawful good is purposed.
If possible, paladins will take service or form an alliance with lawful good characters, whether players or not, who are clerics or fighters (of noble status).
This paints a fairly clear picture: they are holy knights, who seek out service under righteous nobles and kings. They only associate with others who are trustworthy and aspire to righteousness. And they aspire to perform righteous, valiant deeds.
What is missing is an account of what happens if the paladin performs an evil act knowingly but not willingly (the 2nd ed write-up covers that; in the original AD&D context, I'd probably treat it the same as knowingly performing a chaotic act).
What is an evil act is assumed to be known - sacrificing someone's interest or wellbeing, or trampling on value, in pursuit of one's own selfish end. There is less clarity over what amounts to a
chaotic act - favouring one's individualism, over duty and hierarchy, seems a natural enough interpretation.
The two big problems, in my view, endure into later versions of D&D: (i) how does this character fit into the standard tropes of D&D play (eg dungeon delving and looting); (ii) if the GM is expected to judge what counts as
chaotic and/or
evil, than the player is in effect subject to direction from the GM as to how they should play their PC. I prefer the player to be the judge of these things, in discussion with the GM.