just as an example of how you can beat the sim without any clunky mechanics or really short fights(log is private, but here's the ranking info):
Thok the Bloodthirsty 25N 1 496 256 705 1 335 883 918 443.5s - - -
This is our thok kill this week, as you can see is longer than 7 minutes, so there's a chance for a second stampede but again long enough to even it out. the moment of the kill I had 551 Ilvl, 2 pieces t15, no tier 16, no aoc, I was simming 247k on FD.
Boss damage was:
4 - Piichu Beast Mastery 301 116362470 15558015 0 False
262348.3 - 255095.2 102.8% Report is not public
As you can see is a lot higher than the predicted damage on FD. There's nothing wrong or strange in the fight, I got fixated once, 100% on boss. BUT: I had 3 warriors in raid, which is worth 3 Skull banners*3 uses each, which can be added in FD manually in the buffs/debuffs section, but afaik they are averaged, losing a lot of their value. I had 4 Shattering Throws (3 warr+feral)*2 uses each, which means the whole Lust duration, something that FD can't simulate. And of course I prepoted, which in the sim is off by default. Adding all this manually in the buff/debuff section yielded me a 1.8% dps increase, almost 5k dps, still far from the real DPS.
TL
R The dps you get from a default FD run is a good guideline, but you should be able to beat it in a proper raid envyronment