Battle of the Celestial Gates

Perhaps one of the most difficult missions in all three Campaigns, there are too many mutants (but I feel like the developer held back to avoid giving them too many stats, like they did with the bosses in Campaigns 1 and 2).

The map is good, I liked everything)
I'm just curious, how did the final battle turn out to be so easy?

He has a lot of hit points, enough power, extremely high initiative, and he also gets an extra turn with Hellfire, which deals 1k damage to each unit without any debuff protection. He goes almost first, can remove control, Berserk prevents him from dropping the Dwarven Shield, and he has absolute gating. If the Imp gets a turn, it's game over unless you put someone in front of him to take the hit. He has enough defense, the bonus from the Dwarven set works great for him, attack, defense, luck buffs. If you fight him for every initiative point to make sure he doesn't go first, it's even harder. I only won because I had two stacks with control, and another one with high base initiative to fly in and attack the Imp, but I still had to max out its initiative (except for Sandro's Cloak, you can't do without it). And I won on the 20th try or so.