It's odd how sometimes you read something and it subconsciously jars in the head.
Inculta just put a perfectly reasonable and agreeable post about heavy armour that I read and nodded along to: but FOR ME the idea that orcs should have heavy armour is fine in lore really did not sit well.
Dwarves, absolutely. ( and Dol Amroth/ Citadel guard probably ).
A few orc chieftains at Mordor uruk level... maybe they have quality armour.
But over the 50 years since I first read the Hobbit I have felt that orcs - the mass of Shadow infantry - have been successively improved in size, strength and ability. I do realise that both D n D and the Warhammer world have promoted this scaling up and that's fine - for those worlds. But Tolkiens orcs started as goblins: lots of irritating wasp like adversaries, swarming to the attack.
Generally speaking orcs were so inferior to men and elves - that Sauron felt the need to breed/create the uruks to take on Gondor. Saruman with smaller numbers in his army (And possibly copying Sauron too) had to have even mightier and tougher troop types again in his Man-orcs. Yet the 120 men of Rohan took more than 100 or so down in one combat, sustaining only 15 casualties outside Fangorn forest.
So why are orcs inferior? Size for one thing - and TOR does this properly by having reduced Endurance for these types. But I cannot remember any description that orcs were heavily armoured in the books. I think Gimli does ironically complain that he has got a notch on his axe when one orc was inconveniently armoured at the collar*.
As an example of the standard of equipment used by a " huge orc chieftain" in Moria, it uses its hide shield to deflect Boromirs attack before jabbing Frodo with its spear.
Now if a huge orc chieftain is carting a shield made of mere animal skin (i.e. leather equivalent), then the image I gather of these troops is lightly armoured, and therefore faster moving troops: more like cheetahs than tigers. To me, Orcs are more opportunistic ambush attackers: quick to charge in and quick to run off when it gets tough. And if you can accept that, heavy armour just does not fit with the image of orcs met on adventures. For the same reasons our PC s don't often wear heavy mail, orcs wouldn't.
(Wild rant over: @Inculta - its not your post to blame, just my over sensitivity on an old sore point.)
* This idea might be why Orlando Bloom advises the elves at Helm Deep that the uruk armour is thick except at the neck. Darn those films.