I think they run into that amount of fungus which comes at the end of fight which acts as soft enrage when it will be close to impossible to remove it, due to it's fast growth.
We got only total of 2 or 3 haste shrooms, rest were healing one. So we got very close of wiping due to being overwhelmed by fungus. Here's our DPS numbers from the kill:
https://www.warcraftlogs.com/reports...J9pMC#fight=11 (Super and Trolla where on flamethrowers).
We started of being having our flamethrower people keeping the boss area + stacking/shroom area clear and if their flamethrower was not on CD they used it to get rid of the rest as well. By the end of the fight we had both flamethrowers on CD and just had barely enough juice left to keep boss/raid stack cleared more or less. So in the end part of the fight just keep one area clear and specially focus on keeping the fungus away from under the boss. That's all you can do on top of more DPS to end it sooner.
Most of the videos up were from Beta, so the encounter and shroom spawns got tuned abit and I guess that's why you feel that you are getting less Blue Shrooms. Your healer just have to do everything they can to keep the Shrooms up as long as possible.
Also you can try and manage your flamethrower better, by hitting the ESC-key when you are channeling the flame to cut it out when you need to move, so you wouldn't over heat it that often.