Bully works on Slow, Crippled and Knocked Down, but of those, mages only really have access to slow (Midnight Oil, Slow Current, Mass Slow). Rogues and Warriors can get Knocked Down easier, and Warriors can also get Crippled eventually.
Initiative is based on Speed + Perception, which mages don't tend to have in excess, but there is a way to help with that: Put the Leadership ability on your Ranger, and get it to rank 2. Leadership boosts stats (including initiative) for everyone except the character who actually has it. Rank 2 Leadership grants +10 initiative, so that should help make sure that your non-rangers go before the Ranger in the turn order.
The good news is that it probably doesn't matter that much. Status effects last until the turn of the caster of the effect comes up again. So if your mage goes first and lands the effect, you can attack with your ranger. If your mage goes after your ranger and casts the effect, then on the next turn your ranger will go first and will be able to attack before the mage's turn comes up. It's effectively the same thing, the only difference in the second case is that another enemy might clear the effect before your Ranger gets to move, but that's not a guarantee.
And yes, Bully is good. Have your mage apply Oath of Desecration on your Ranger for a further +50% damage.
