i would really like to see a screen of those 390+, for max. peak it's too low and for average prolly too high (although i was never able to test how high a bard could get due to our monk who drains his tp like no one else i've ever seen before xD)
Bard on 220 is bad even with full i90 + i95 weapon he should atleast get 270+ (depends on how tp/mp hungry the group is).
Things like doing Towers or Homing missile are no excuse for losing dps in t8 since you are able to keep your rotation up for 100% of the fight duration (only exception is repelling shot if you're using it to get away from the group with homing missile but even that it's a minimal loss of dps).
And for the potent poisoning potions, if all 8 players use it at the start and whenever the cd is rdy again they would gain about 70k dmg over the full duration of the fight

so about 7% of the total HP^^