I completed it without using summons (I acquired vampirism but never used it :)), the main work was done by secondary heroes, leveled up by the main hero-mentor, in particular Arantir.
When capturing the dwarves' garrison (which initially had 7k dragons and the number increased), it resulted in a loss. I had to reload and escape, leaving only one mountain guard in the garrison.
Otherwise, only one thing bothered me: I didn't know anything about the Titan quest, I didn't get the dragon armor and didn't see it, which is given as a reward for 7 dragon items. And the absence of that coveted mage staff on the map - is it intentional, or was I just unlucky?)