Maybe the most useful advantage of anchoring cosmic Good and Evil as magically aligning to the table's definition of what is good and evil IRL is that it allows for questions like that to be answered easily.
DM: "Does anybody around the table thinks cannibalism is cool?"
Player: "..."
DM: OK, cannibalism is evil and lizardfolk or hyenafolk are evil.
No need for justification, a local consensus can be adopted even if it's not after a long debate on morality.
Jane, a player: "sorry everyone, I can't make it for next Friday's game."
DM: "drat! on the other hand, that will free a seat for Dave, who was looking forward to discover TTRPGs"
Dave: "Actually, I find that cannibalism can sometime be justified on the basis of tradition"
DM: "OK, it's neutral, then".
Kelemvor: "Please listen, souls, we got a cosmic update, if you engaged in eating sapient species, DO NOT follow the line marked "Gehenna" or "Baator" as you were in fact neutral, instead follow the line marked "Mechanus" and "Arcadia" respectively. I repeat..."