Necropolis – “Misfortune never comes alone” [Campaign 2 – Mission 1]

Well, my enemy's army is roughly 2-3 times larger than mine; they simply have more troops. Despite this, I've only lost 10-15% of my forces throughout the entire game, reaching his castle. After capturing it, the gates open, and heroes attack us from two sides... These heroes, combined, have almost 4-5 times more troops. They simply overwhelm us with numbers, and there's nothing I can do...

Could I face difficulties in completing the game due to the lack of dynasty bonuses and other similar advantages...? The game hasn't been purchased yet.