Trolls

It appears that the intended role of the trolls was what we see. Something big and strong that can be an effective shock troop. They were meant to get in the middle of a huge group of enemies and hold their own. Not just hold their own but completely dominate. After all, they were initially used as balrog bodyguards. There is no point in having a hobbit protect a balrog against an army of elves and dwarves. Lastly, Sauron later needed a beast of burden to handle the Black Gate and his over sized weapons.   Prior to the creation of trolls, there actually other creatures able to fill this role. These were balrogs and dragons. Both were much more devastating than trolls at an individual basis. Dragons appear much tougher to kill and have the benefits of fire breath and flight. So trolls do not appear to have as strong of a need for their creation.   Trolls have many benefits though that justify them though. The trolls are much more effective as beasts of burden. They can also be bred so losses can be replaced. One of the major problems with balrogs is that each loss in permanent. This is also faster than dragons. While we have no hard numbers, we can assume that trolls are better on this front. Simply taking decades rather than centuries to be fully effective on the battlefield makes them better. This allows them to be much more common and thus useful in combat. Just as important is upkeep costs. A single troll would require much less space and food in order to keep alive.   Their design is actually much more practical in their role than the balrogs and dragons in one key respect. Their size. Yes, they are impressively large. But not too big to be useful. The trolls in Moria would not have been a threat to the Fellowship if they could not get through the doorways or move down halls. The same problem materializes at Minas Tirith. Yes, the front gate is massive, but all the others are much more conventional sizes. Which means troops too big and they would not be able to penetrate. Thus, if one wants shock infantry, one needs the trolls to occupy the middle ground they do. Big enough to be scary and easily overpower enemies, but still small enough to get everywhere the army needs to go.   Where they shine the most is in their lethal potential. Their bulk and strength leads them to be brutal. Their raw physical power can blow through practically anything in their path. The power of the thrust a troll should be able to impart with a spear should have been able to kill Frodo even with his mail shirt. Then they have the added benefit of being super difficult to kill. It is possible, but appears to take a significant amount of firepower to pull off.   Yes, there are improvements that can be made on this front. Primarily by borrowing elements from dragons. The first is the adoption of dragon scales covering the vital organs in the front. As they stand in official media, their scales are softer than dragons and only occur on the back. Do they really need it? Technically no. But it would make them a lot more powerful. Nor does not need to cover the whole body - just the areas most likely to suffer major blows. Perhaps one does not need to be totally as hard either. Just increase the resiliency of the scales and place them in more useful areas.   For trolls meant for attack roles, more dragon like claws would be beneficial too. I'm not saying their existing ones are bad - they can dig through rocks. Nor am I saying hands should be foregone entirely. The more labor oriented breeds should retain their more human hands as those are better for work. But hands more akin to eagle talons would still allow extremely powerful grips on weapons that are better weapons themselves should the lose their weapons.   In terms of terror, they are similar to orcs but better. It would take many orcs to have the same mental effects on enemy troops as a troll. Hence their utility. Their sheer power though provides two additional benefits that orcs do not. The first is they can scare the orcs, thus allowing for keeping them in line. Then there is the drums we see them use. These can increase both the terror they inspire in the enemy and aid in command and control.   So the original trolls were almost impractically stupid. But this appears to be fixed in Sauron's upgrades. These Olog-hai were able to understand full languages and perform much better swordsmanship. Thus, they can be much better soldiers. But even these upgraded soldiers appear to suffer serious limitations. We never see them engage in anything truly complicated and they seem lost without purpose after the One Ring gets destroyed. So it seems difficult for me to imagine them being smart enough to organize a rebellion.   The above mentioned improvements stem from the fact they have thousands of years of battle testing. Not to say their original design was bad. They appear to have actually performed decently well in their initial outings. Just combat appears to have highlighted some of their limitations, hence the utility of the trials by fire. And Sauron learned from this and improved based on experience.   They do not appear to have a dedicated fatal flaw to exploit to prevent rebellions. In fact, if they do turn, there appears to be nothing to slow them down. Their intelligence appears to be the prime means of control. Being dim witted apparently makes you easier to mind control in Middle Earth. So Sauron was able to use his normal but One Ring enhanced mind control powers to control them. This is a potentially brittle form of control. They might not be able to organize mass uprisings, but there appears to be nothing in their design stopping them from taking individual actions.   Overall, this means to me that there would be possibly be threats to the poor orcs near them and unusually cruel masters. They could act on their own in moments of rage or fear. They might even bring down a large number of the forces sent to control their rampaging. But that is all it would be - individual rampages. Each would be costly but too inchoate and isolated to be a risk to the regime.