It can help you decide for yourself for your strategy you can build as many Tribute camps as you want and you can choose one of the 3 factions, but remember that the Tribute camp will not gain resources and doesn't fire arrows, so it is vulnerable to attacks in which you need to defend by units or summon Barricade and I don't think it's easy for a player to build 6 Tribute camps and spam calling since you will be building slave farms for resources as the Tribute camp doesn't gain resources. As I said this will make Mordor more of an offensive as its strategy is to conquer and build Tribute camps, morgul and dol guldor fortress, I think Tribute camps will be very useful since it costs 3000 to build a morgul/dol guldor fortress plus in order for Sauron to use influence he needs to be level 3 which I usually receive by recruiting Cirith Ungol unit and a Nazgul which altogether costs a lot that's why I think instead of Sauron's influence needed for Tribute camp in order to call Unit 2 it's better to make it a power instead. Mordor is lacking in cavalry you only have mountain trolls which cost a lot along with the troll cage and the Haradrim reinforcement power costs 7. Playing against Gondor can be a little hard as Gondor can build cavalry easier and cheaper along with stronger units that can be armed as well. They can spam archers until the building gets level 3 and purchase fire arrows, if you don't have cavalry at this time your toast because the orcs become useless. Gondor's cavalry can be even more cheaper since you can build farms inside the castle or camp, but when playing Mordor you can only build Slaughter houses in settlements or Outpost I think. Not to mention that Gondor has signal fires and can have allies armed and increased which makes them stronger.
I also think that Sauron's influence on Towers should give Barricades fire arrows.
Gondor's cavalry can be even more cheaper since you can build farms inside the castle or camp
Sorry I made a mistake about this statement. Gondor can't build farms in castles or camps.
Since the new update made a difference so you can get Trolls cheaper I think that helped for cavalry support. it makes sense that Gondor and Isengard need to upgrade barracks and other building since they have economy boosting buildings and upgrades. I think we should have more to the Arsenal building. Maybe make Sauron's influence unlocks other upgrades than fire arrows like Armed Troll upgrades and make Sauron's influence on the Troll cage Unlock Troll porter (If you remember him he was in BFME 1 evil campaign in Harad) maybe we can put these call powers in the fortress and it has to have something to do with Sauron's level, for example if he was level 2 you can call Rhun reinforcements from the fortress. If he is level 5 you are allowed to call Umbar reinforcements as well and if he was level 8 you can call Harad.
The Troll porter can be used in a specific way. First of all he will cost a lot of resources since this strategy can be overpowered. When you recruit him all you have to do is send him to one of your Tribute camps and it will be Upgraded to a little different design building. Each upgraded Tribute camp from Troll porter will increase allies by one battalion, however this can be difficult to achieve since you need Sauron to use his influence on the Troll cage and then recruit the Troll porter which costs a lot maybe 1500 or maybe more. Upgraded Tribute camps from Porter won't just necessarily increase the troops, but make different type of units to make it balance. For example if you are calling Harad with 2 upgraded Tribute camps from Troll porter units with 1 Mumakil will arrive. If 4 Tribute camps are upgraded 2 Mumakils will arrive and if 6 are Upgraded 3 will arrive. I thought of this because even with the call Harad and Rhun powers you cannot have access to Corsairs Unless we can remove the Shelob power and replace it with a call Umbar reinforcements.