any screen shots of a completed run you could share, frozen banshee seems to really shine more so in counter attack teams with the extra attacks and extra chances to place poison etc 

im running her in my alt account with no counter and no extensions and she is definately noticeably down with out either mentioned

are you champs fully mastered?  

i would give kael a run with frozen banshee just to see if you can stack more poisons with the poison sensitivity but your concept is right  with dec defence, reliq with revive and heals, you have rear guard sergant who can offer dec def, dec attack and contious heals who would be handy early for you  

have you tried kael lead for hp aura, rearguard seargant for dec def and dec atk, frozen banshee, kael and reliq tender as a team yet? 

having kael and fb might be able to fill your debuff bar with more poisons, once you pull a counter attack champ your damage will jump 

bulwark is a handy champ early to as he has HP burn but also when hit chance to increase debuff extensions