I messed with direct x 11 and 9 settings and when in dx11 mode it dropped by 5-8fps in that mode (other settings I messed with at that time (other than bloom of course) were fullscreen vs windowed maximised. Also with one of them I get 100% of my gpu being utilized (as opposed to 70-90%) so I think is fine now (as in not a horrible drop considering bloom isn't really a light rendering aspect). Cryptic must of updated the bloom quality, I think I noticed somewhat of a change anyway.
I've always had a huge frame rate drop on maps with the large white blooms. Especially the Mirror Universe incursion maps (although I read somewhere that the blooms were removed from that map finally).
This goes back to before Season 7. I just think that Season 7 introduced more maps that include these kinds of video card killing blooms.