I think most of my views are taken from my own group's experience... we've currently downed Styrak 3 times so far and each time we've always hit the enrage, yet technically we should have more than enough DPS by your calculations (if we go by Dummy numbers).
Currently trying to figure out if it's a DPS uptime problem or simply a DPS translation (from Dummy -> Boss) issue, but personally i'm going from ~2.5k-2.6k on a Dummy to ~2k-2.2k "during" and 2.4k "after". Although my numbers have been increasing each week, so it could possibly be i'm not familiar enough with the fight yet.
Are you sure your tanks are pulling their weight? Your healers? What about your other DPS? Numbers drop a lot with uneven DPS compositions due to the four adds mechanic.
I've observed that a lot of specs plummet on that fight. Anything with the word "Lethality" in it is in really bad shape due to the frequent debuff cleanses. Conversely, some specs see a nice buff. Infil shadows do worlds better on Styrak than on a dummy.