Why? Please, elaborate.
It's not a given that you'll have to fight in a Castle!
A tent with skilled machine operators and first aid will be very helpful, but a ballista without fire arrows seems like complete garbage to me!
And another thing really annoys me! The bears roar almost after every one of their attacks, it's a total rip-off, and they also constantly take Soldier's Luck, which greatly increases the chance of a roar. This roar not only scares away my warriors but also lowers their initiative. How can I deal with this?

Avenger is right, take pure Rage! Firstly, the bear's roar is calculated based on the ratio of the total health of the stack, meaning if there is a lot of Rage, the bears will do little damage, so there will be no fear. This is the biggest increase in the Orcs, meaning the Orcs will have more total health, and they won't scare anyone!
And secondly, if you have the amulet, you can raise Blood Fury to level 3 at the beginning, and don't forget, that's a huge bonus for the unit! Some Cyclops have an Aura of Terror and an Aura of Fear, so if you hit four of them at once, they'll all run away, especially since Gnomes like to cluster together, they have hydra defenses, and how many units get +2-+3 initiative, this gives you the opportunity to strike first without using a rune! And if a Gnome doesn't have time to use the rune, it will quickly fall apart from an Orcish attack!

Added after 18 minutes
KITOBOI, are you playing with a mentor?