No, I would just make the orogs or orcs of a sufficiently high enough level to challenge the party. Ten orcs who are high level fighters or barbarians are plenty tough, no rewriting of the rules necessary, though I am more than happy to home brew monsters as needed - doesn't everyone? Never been a problem. There isn't an argument you can make that is going to convince me that what is happening at my table is not really happening at my table.
sigh and this is the Elminster problem in reverse.
Let's say you have ten level 12 orcs who are an equal match for your party. Who are they? Well... they would probably be chieftains, right? After all orcs rule based on strength and these guys are clearly enormously strong. In fact, they are so enormously strong, it is really bizarre that they are all ten working together for the sole purpose of hunting YOU. They've made some sort of orc alliance? Were there even ten tribes that powerful that you foreshadowed in anyway? Because since they made an alliance to hunt you, it is logical it is because you killed orcs and scattered tribes, so how did you only fight weak tribes until THESE guys took notice of you? And they made an alliance.
But, let's say you make a mistake, and instead of saying they are from ten different tribes, they are from a single tribe. Now, why is that a mistake? Because orcs rule on strength. So therefore you have to have a single orc leader STRONGER than these guys. Otherwise, one of them would be the leader. Or maybe one them is the leader, it is the lead orc and his honor guard of equally jacked warrior orcs. Problem solved right?
Except, again, a force like this is immensely powerful, he would have to rule a tribe greater than any other. Did you world build that? Did you place that tribe in the world, ready for this event? How have they not swept aside cities that were earlier threatened with destruction by lesser foes your party defeated?
Sure, you can ignore this, you can sweep this under the rug, or maybe you are skilled enough at winging it that you can plaster faster than the player's care to ask questions. But generally? Generally people want to know if they have put world-shaping power blocks into their world, where they are, and what they are doing. And to do that, you sort of need to know if a group of level 12 orcs is anything exceptional. And by most DnD standards? They are. By official declarations, a level 12 group is a world power. A weaker world power, but a world power none the less, and it doesn't make sense for them to be just random brigands.
As for the game being about expectations, I could care less about anyone else's flavour texts when it comes to the story we want to create.
This isn't just random flavor text, it is what the rules lay out. I don't get your insistence in saying "well, if I want normal starving bandits who can punt about demon lords, then that is what is going to happen" and ignoring that the game does not naturally support that as the progression.
LotR is the ultimate fantasy archetype in general. That's not really debatable, is it? It's like saying the Beatles are the most popular rock band - you don't have to like them to concede, "fair enough." For the record, I am not the biggest Tolkien fan, but I went with an example that everyone knows.
Of course it is debatable. Heck, you say the Beatles is THE most popular rock band? Yet a quick search shows that The Rolling Stones, Pink Floyd, Red Hot Chili Peppers, Queen, and AC/DC are also in competition for that title. The Beatles are the most FAMOUS, but that isn't the same as being the most popular.
And using something the "The ultimate" isn't even appealing to the popularity or how famous it is, but trying to claim it is somehow the best fantasy archetype. Which is HIGHLY debatable.
My point is that, for the Fellowship, including Gandalf, a bunch of orcs and a troll are still serious threat, one to be ultimately fled from. Then they run into an even bigger bad, sure. But Gandalf couldn't just laugh off the first threat. The stakes still feel real in that fight - Frodo almost dies.
It is not remotely hard to make encounters for higher level characters in D&D that still feel grounded. I mean, for me, anyway. YVMV.
Wow! Frodo the baddest bad-ass warrior in the entire fellowship! Oh wait, no. The guy who is the equivalent of a rich middle class highschooler whose been in, what? Two fights by this point, nearly dies in a fight? Clearly a sign of desperate times and dire straits.
The fellowship defeats the troll and the orcs in moria, then runs from ENDLESS MORE ORCS. And, again, you need to put the Fellowship in DnD terms. The Fellowship is not Nine DnD characters. Sam, Frodo, Merry and Pippin by this point in the story are not fighters. So you really only have five people who can fight. Gandalf, Boromir, Legolas, Gimli and Aragorn. And yes, they struggle against the Cave Troll. In DnD terms, what would the cave troll be? Would it be equal in might to a Dragon? No. As powerful as a Beholder? No. It is, at best, a Hill Giant. A CR 5 threat. And it is, as you point out, a dangerous threat to Gandalf and the others.
In fact, Dragons are a great point. Smaug was not an ancient dragon, he was considered young. But even if we make him a full adult Red... again, Gandalf never once considered the act of fighting Smaug directly. No one did. It was considered suicide. But fighting and killing an adult red dragon would not be considered strange for a mid-level party, and might be considered too easy to even bother doing for a high level party.
Tolkien may have made good fantasy, but the power scale of DnD is FAR FAR beyond anything in Tolkien. The things that the Fellowship did as great acts of incredible skill and bravery can fit into a level 5 character. And this MATTERS, because the world building needs to understand what is a threat to whom. You don't have minor demons as a true threat to a powerful archmage, and you don't have a bunch of farmers beat back a mountain-sized colossus powered by god-magic.
