Cysticfury

I'm kinda new to CoH have a level 50 SD/BA and Its so rare to see BA as tanker secondary.. but almost every BA power has knockdown am I missing something? why is BA so unpopular for a tank? and it hits REALLY hard!! I mean it does have slow cool down but still... I have been looking for guides on how to slot and there is Nothing.. should i just use a SD/WarMace guide?