With BM as 1st, in the beginning flame is perfect against archers,ghouls,milita because you can kill them fast and your experience jumps higher and higher.Against hunts it works but when you have sorceresses to slow all hunts,they cant escape and you can cast flame many times,then they are owned with rifles.
By the end of tier1 you can quickly reach lvl6 with flame and own.But if they reach tier3 and you have casters the polymorph will work too.I told you that you need casters even for tier3 but not only casters.
The BM is good for both AT, teams and FFA (in most cases) but not for solo.You see in those listed game types how useful he can be