Tactics against Brontors...

[Zechnophobe]

sheep the brontors, and they are still spikey, but at least they won't do normal attacks. You can use abilities like dragon power, and fire line attack (red dragons) and they won't damage you.

You can also Helplessness them to make them easier to kill, or pygmy. Ball lightning though is probably the best choice. It's the strongest rage ability for a mage (maybe mana accelerator.)