Fire isn't devastating. It sucks. They are really easy to counter. Let them throw fireballs at the same unit (I'm assuming you are saying they take advantage of the lore attribute). Think how devastating it would be if the DE player spent 500 points on death instead? Fireball without die limits - so throwing over 6 die at fireball is good - no offense man, but that is kind of smoking it (see what I did there?).
Like I said, BG are dangerous, but less so to us. But is they get in with something not SM/WL/PG, then trouble brews on the horizon - moreso if they take hag graef instead of murder. If you think that they are no big deal - then I believe you opponent must be running them suboptimally. If hey get into combat with our specials, we win, but if they get into combat with anything else (or buffed up/us debuffed down) they toast things.
Oh, only once per spell - not a big deal then is it? They can get off a lot of spells = lot of extra pd.
Yes - we get rerolls. They way I look at it (when we are not fighting each other) is that we always strike first and usually reroll but they usually strike first and always reroll (at least in the 1st round). But they are cheaper across the board and we don't get rerolls if we are fighting black guard/cold ones or if we git hit with miasma.