It occurs to me that, by showing the dwarf origin story, we get the opportunity to make all of the key/important points needed for the (unshown) orc origin story.
1) We will see Aulë create the dwarves, so we will know what a skilled Vala can do 'from scratch'.
2) We will also see that these creations are puppets/golums with no wills of their own. They don't have to be robotic or 'yes, master' about it, but they should very clearly be....on strings.
3) Only Iluvatar can add the spark of life (from the Flame Imperishable) that creates true Children (elves, men, dwarves) who are as free as the Valar/Maiar to shape their own lives.
Knowing this, 'What are the orcs?' remains a mystery, and it depends on our depiction of the orcs as to how people might answer that
. I think that it is important that orcs have speech *and* be totally depraved. Which suggests that Melkor bred some Maiar into his beasts and made them humanoid...or tortured elves as part of the breeding stock for orcs. Or something along those lines. But if we don't say that and don't show that, and make it very clear that those telling the story *don't know* what happened...it remains a mystery for the viewers to discuss amongst themselves
The most that should be said is that Melkor searched for the Flame Imperishable and coveted it, but never found it for himself.