450 is way to high, the only legit method I could see working is allowing players to either gain more soldier tomes by going on needed role or having it where the tank and healer role can gain an extra 50 poetics for playing said role.

So instead you would have this.
Base poetic gains=450
Tank role gains=50 cap
healer role gains=50 cap

This way you are only offering a slight advantage of playing a healer/tank role rather than offering a incredibly huge leap of gear gains in a sort period of time because in essence you are recommending that what is suppose to be earned in 3 weeks of play will now be earned in 1 week and that would destroy the pace of the poetic gear gains.