I'm just mulling over this--it saves me going and trying again, which I can't face doing at the moment! Anyway, my mulling concluded that it's probably something that people who are good at multi-tasking find easier, and people who struggle to be observant or attentive struggle with. I think to get through easily, you need to be observant and methodical to spot the ballistas and so on that need to be taken out; you need to use the new weapon thingy to take out clusters and keep an eye on its cooldown; you need to use the "summon friend" and keep an eye on both its continued existence and cooldown; you need to alternate between fireball (and its cooldown) and dragon breath; you need to keep an eye on your health, the Zeppelin's health and its position; and in doing so you need to remember to use the heal spell and potions and keep an eye on their respective cooldowns; you need to remember to use decent armour instead of the "placeholder" set it gives you; and a bunch of other stuff I can't even remember.
Given my difficulty concentrating on one thing let alone several and the impracticality of looking around and taking stock, I suppose it's not really surprising that I've yet to complete this section successfully.
I wish they'd given an alternative means of completion so I didn't have to do this, however, because even if I do complete it I won't have enjoyed it. I believe I mentioned that I hate escort quests!
So please, Larian, give us an alternative means of doing this stage at some point. Or at least give us a Zeppelin with thrice the hitpoints!