The point there was to try and draw a distinction between the normal actions of the orcs, which I agree any sane person would define as evil, and the fact that they are defined as (usually) evil by their alignment.
But the only significance of that definition is as a shorthand for their personalities and behaviour. Because that's what alignment is.
My own preferred account of D&D alignment is found in Gygax's AD&D books, but the same thing is said in the 5e Basic PDF (pp33-34 ):
A typical creature in the worlds of Dungeons & Dragons has an alignment, which broadly describes its moral and personal attitudes. . . . These brief summaries of the nine alignments describe the typical behavior of a creature with that alignment.
So to say that orcs are inherently CE is just a shorthand for saying that it is in the nature of orcs to "act with arbitrary violence, spurred by their greed, hatred, or bloodlust." (Quoted fro p 34.)
Does that warrant killing every orc you meet? That's a further question which is not answered simply by reiterating the point that orcs act with arbitrary violence out of base motivations.
When you know something is evil, you don't have to agonize about killing it, even if you yourself are good.
Don't you? Is the only reasonable response to base and aribtrary violence the use of lethal violence in response? There are well-known moral views in the real world which don't accept this proposotion, and not just pacifistic ones.
The fact that relatively little D&D play reflects or conforms to those well-known moral views isn't explained by reference to the fictional state of affairs whereby orcs are said to be evil - which is, as I've shown, just a shorthand summary of their outlook and behaviour. It's explained by reference to the real-world state of affairs which is the tone and content of mainstream fantasy fiction.
D&D would be a very different game if the players had to agonize over the ethics of killing every monster they meet. The point of 'monsters' is to not have to do that
The notion of
inherently evil does no work here. What you say here is just as true if the PCs are assaulted by some bandits on the road, or are assualting a cultist shrine hidden in a city basement, as it is if the PCs are fighting orcs.
The game is premised on the relatively casual use of violence being morally permissible. You don't need any pseudo-metaphysics of "inherently evil" to explain that. In the real-world periods which provide the general tropes and trappings of fantasy RPGing the casual resort to violence was also pretty common, and no one supposed that the human beings they were killing were "inherently evil". They just had a very permissive view of what sort of violence was permitted on the grounds of defence, retribution and otherwise to enforce considerations of justice.