I struggled with alignment for decades as nothing ever satisfied. There was always something that didn't work for someone ... until I just stopped using it without telling people. If I were to revise the game, I'd just drop it from the rules as obsolete. I'd still have the concept of evil - but no mechanics tied to it. Rather than have an alignment in the monster entries I would have 5 adjectives to describe the typical mentality of the creature. Which is more useful to a DM in a stat block for a burrowing beast: Unaligned or patient, tricky, timid, hungry and industrious.
Here is how I handle it when it comes up in the limited ways it does still:
1.) Alignment is opinion, and the opinion that matters is the one granting the magic that is making a determination. Do the ends justify the means? Do you make the decision to pull the trolley from killing four to killing one? There is no absolute answer, so you need a judge. Thus magic from a cleric of a Duty God and a cleric of a God of Freedom might find different results from their magics that evaluate the alignment of a person that willfully broke an agreement and betrayed allies in order to free criminals that had been given life sentences for relatively minor crimes so that they could work in the mines for the king.
2.) Just don't bring it up. If the players ask an alignment casually, shrug. If they use magic to determine it, see above. But as a DM, just don't make use of the magics that trigger off of alignment. There are plenty of other ways to use spell slots and other resources that might trigger off of alignment. When NPCs refer to evil and good, have it generally be to the absolutes in the games: Celestials, Fiends, etc... Make sure that they're referencing the absolutes.
