Every time people lament changes to the lore that amount to "not every member of species X is irredeemably evil" and claim the game is removing villains from it, I think how villains of so-caleld evil species fall into two cathegories: a) bland and boring and b)have something else, unrelated to their species going on for them, that makes them interesting.
I'd argue Devils, by their nature of being lawful as well as evil, are often interesting villains because of their "species", but it's kinda different when it's a creature literally made from the primordial essence of Evil rather than just a bad dude.
No, equating alignment and morality makes them both meaningless. Morality should be tied to outlooks/philosophies etc, a personal matter of how the individual acts in a situation, while alignment with the forces of good/evil/law/chaos should be a matter of absolute determinism. It's easy to look at D&D and say it's wrong, but just because something's bad in D&D doesn't mean the idea itself is bad.
I have it to where the good/evil extraplanar creatures are created as expressions of the good and evil within everything sentient.
Yes, exactly - as I put it to my players, a "person" isn't able to be inherently good or evil. They'll have their own morals - particular things they always will or won't do - but alignment is for things literally made of the concept of that alignment.