OK, so first off we're talking about FDK pre-raid BiS for Lord's pre-Naxx pre-T7.5. You said it yourself - BCB is wep dmg based, ArPen based and Haste based. You don't have much from any of these at Naxx level. Honestly, Naxx is the tier with the worst possible plate gear available on WotLK. I wouldn't call the 9% crit from Subversion "redundant". Obliterate is an important part of your DPS, is your main RP gen, your FU rune dump, and your Rime proccer.
So in the end, getting back on topic, at pre-raid levels Subversion > BCB. At BiS levels BCB MAY be better, but even then - god, I ****ing hate FDKs without Subversion taking my aggro as tank in case they're not even in Top3 DPS.