Here are the problems with caster survivability from what I see:
- The combat arenas are designed for close-range combat so mages have to be close range to engage.
- Rules Change: Maximum Range of long-range spells and arrows is 60 feet (18m), down from 120 feet. A typical character can move and dash 60 feet to get right next to your caster, in AoO range. That's no good.
- The AI still has the D:OS tendency of preferring to target weaker/low AC characters, even if there are larger apparent threats closer by.
- Too much AoE damage from thrown object spam, and surface damage.
Wait until level 5 when Wizards and the likes get Fireball and can take out a good chunk of trash in one single action. And it only grows from there.
What trash? Spell damage has largely remained the same, but enemy HP has increased.