honestly if you're gearing for full fire damage and trying to run around spamming fireball you're pretty much trolling your team. mage from a strictly offensive perspective is better off focusing on control and enabling your teammates to connect and land kills rather than trying to do damage yourself.
it's probably fun to stand around trying to do big fireball dmg in one-sided pug midfights or something, but in a somewhat balanced game, realistically no one is gonna let you afk in the back turreting max rank fireballs. pushback is brutal on mage and you can't afford to stay stationary for long periods of time otherwise you'll fall behind the play. all it takes is one hunter pet or a level 12 bear form druid hitting you and your fireball cast is now 3 weeks long