I don't think TDB has ever 1hit someone assuming equal level and equal kits.
It has however one hitted people (from my experience) when they are yellow poisoned.
Perhaps yellow poison is the problem. I'll be honest 90% of the PK's I get on warrior are due to a yellow poison tdb follow up by another TDB or FS.
Proposed change:
What about instead of yellow giving x1.2 damage (for warriors), instead make it do what it did on Euro: for the duration of yellow poison, you cannot cast spells. I feel this was meant to be the initial point of Yellow poison in the first place, not the extra damage it did. Would stop end-game warriors being so strong with that x1.2 damage boost, but at the same time still be very very useful.
Now the question is, do you make sins flashdash do the same effect or not.
As for wizards...
Well, I've been saying they needed looking at for a long time. Any class than can hit 450+ damage in a 3x3 aoe is just outright broken.
How do you go about fixing this?
I liked Razurus' suggestion. Make it's damage be dependant on how many things it's actually hitting. This would in no way nerf wizzies levelling speeds too, so it's a win win situation.
If you're using FlameField to hit just one person, it should not be doing 400+ damage. If you're using it to hit 3+ people/things, it should be doing 400+ damage. This brings strategic play into account. You would need to put yourself into actual risk to do serious damage. Running up to a sin or archer or tao is not "putting yourself at risk" as a wizard currently.
Those would be my suggestions. Take them as you please.