Cant beat Cliffs of Sordünn

I have tried this level five times now and cant even come close to beating it. Every single time I get around 3-4 cities made and have 4 stacks of 6 units ranging from 600-800 power level, Merlin and his Vassal will each already have almost double my amount of units and higher power levels.

The best I have done is taken over 1-2 of the vassals cities on the main continent, but Merlin or the Umbryal Abbys will come and destroy me while I am busy with the Vassal.

Julia is also completely useless. She doesnt really done anything to help. Makes a few stacks, sends the across the sea and dies instantly.

It feels like a 1v3 fight with Julia watching me suffer.

Advice appreciated