I agree, Arlemus, that both the Forcemaster and the Warlord suffer from their weak schools more than any other mage. They are the only ones that are actually required to dip into their weak schools in order to make a viable build. However, the Forcemaster's play style is much better supported by the current card pool. She was actually considered overpowered for a brief time, before errata to Battle Fury. Her power has been in steady decline since her release, however, and the weakness for creatures is definitely holding her back from where she would otherwise be, but she remains viable because the cards still support her being super aggressive and killing her opponent before they have time to properly respond.
In comparison, the Warlord seems to want to swarm the field. There's already debate about swarms even being viable, and so many people would consider that to start him off with a handicap. Then you add in that his spawnpoint has not been considered very good, and his swarming play style goes down the drain. Finally, his Veterans ability is somewhat subpar because he has no control over it or any way to predict it's usefulness. It depends entirely on what strategy and creatures his opponent decides to use as to whether it is any good. All of the Forcemaster's abilities are good. The weak school tax definitely exacerbates things, but it's not the only thing.
That's taking a look at how things stand pre Forged in Fire. The errata to Garrison Post and all of the new cards being released will definitely change the playing field. But you are correct that the weak school tax affects both the Warlord and Forcemaster, it's just that there's a lot more going against the Warlord. I do not consider him unplayable like some have stated. I've seen him do very well with an Elite Squad of troops. However, he is definitely the most handicapped of the mages.