What I mean is that there is a qualitative difference between what the kids call fluff and crunch in the monster stat block. Within the fiction, a group of 4 orcs might have leather armor, or they might all have full plate and a shield, and neither choice makes more sense than the other. But a difference in 3 or 4 in AC is very important for the math of the encounter. So, to the extent that the DM is relying on the math of the stat block (as a game element and not just part of the fiction) the difference between leather and plate is meaningful. The fiction of the encounter has an equal impact, but is more variable as it depends on the dm's ability and interest in roleplaying. For some people, alignment is helpful in that regard and that's fine.
Honest question in that regard: the npc stat blocks in the MM and Volo's have "any alignment" instead of a specific alignment (e.g.
Priest,
Veteran, etc). Is this a problem for you, that there's no baseline for these statblocks? How would people feel if in future supplements humanoid creatures also had "any alignment" in their stat block, while fiends and undead and so forth still had alignments. In this way, alignment would still be part of the metaphysics of the implied setting, but humanoid "monsters" would get to have the same range as the human-elf-dwarf-halfling npc humanoids.