There is no real balance.MA has all the advantage.they have high, consistent damage. They can maneuver while dpsing. They can heal and use magic shield.
If you are a fat MM then you can out-heal the MA damage to your horse. However, if he starts shooting at you, you’ll be hard pressed to survive. All it takes is a few interrupted heals and you will die.
You can try go full offence but it will be a dps race and again if you get interrupted too many times you'll die. Its a dice roll situation and it will depend mostly on how many shots he misses. If he hits every shot you’ll probably die before you can put out enough damage.
You can try and go for EQ, but any good MA will just stay far enough not to get hit.
If you have necromancy, and are able to get close to the MA or even on his right side, you can do some serious damage with awe surge or death hand. Just dont miss, and use his blind spot to your advantage.