Lvl 37 half-elf, and although the changes over the past few months have made me weaker, I can still defeat yellow solo mobs 75% of the time or better and green groups most of the time. I also have some problems with casters, using Arcane Symphony sometimes helps but I just get whooped a little bit slower. If I have to beat a difficult caster, such as the lvl 31 ^^ skeleton for the final part of Cove of Decay access (forget his name) my best bet is to resist as much as I can and drain their power. Once powerless, they are normally easy to defeat even if I too am running out of power.
I should probably mention also that I use Ghoulbane and a shield for soloing, as well as using defensive buffs as opposed to attack ones such as haste. Using DW and trying to take down the mob quickly doesn't seem to be as successful for me, but others I know seem to find DW works better.