Yeah I agree with Borella, you can get past very easily if you have a mage or priest with you. They each can one shot the flames as long as mages have Electrostatic Charge on, and priests have Holy Aura on.
Now what I do is that as a mage I know the guards will take out my electrostatic charge, so I take on the guards, run away, kill them, put on my charge and run back in and either take the tower since I wont be effected by the flames
or kill the traps if I have teammates.
I think traps in siege need a big upgrade from what they are now, they don't offer much in protection. So I think they need buffed up in health and all traps need to hit more than 500.