[Alneyan]

Hand of Death can be good for your mages, as it deals a lot of damage bypassing armour... but you will need to get your mages at point blank range first, and Death mages will probably cast other spells than that one when under AI control. I don't know for sure how Decay works, but it could be a solution: you have access to Bane Blades, the Decay spell and Banefire, and those deal a lot of damage at the end of a battle (hitting the Sphinx will not be a problem).

The main factor for Dominion spread is the Dominion level you picked when creating your Pretender: the higher it is, the more easily your Dominion will spread. You should aim at having 6 or so for a good spread, and the AI seems to pick Dominion levels around that value too. You can raise Dominion in one province by bringing in your Prophet and your Pretender (who automatically spread Dominion), by building temples in the immediate vicinity, and by setting your priests to preach (they only raise Dominion when preaching). If it still does not work, a few units have the ability to lower enemy Dominion (Sceptics and one Demon Lord, in particular), and the Stone Idol has the same ability, so it might work out... if you can get any of these things, as they aren't particularly easy to reach for Machaka.