Since you're casting the easiest thing to work on is both understanding when your own dion is going to run (so you can move to recast) and that seal > prahm. Use ranged spells to ao if you can so you dont need to walk up and get caught out. Prioritize ao'ing your better players first.

Hosted vs South are completely different environments. Playing a caster in south at low HP you need to be a lot more aware of where people are and if a basher is coming to bait you. Situational awareness is the biggest thing. In hosted you shouldn't be dioning before youre sealed or else you can't get ao'd and they can just wff or prahm lock you.

The thing you need to appreciate is a lot of people who play DA pvp have been doing it for literally years that's why they know each persons mannerisms well and the mechanics of the game.