Your damage is not as bad as you think.
First of all you are attacking spore shooters more then an average number hungry flame throwing hunter. I picked at random a hunter with a similar iLvL. Look at the damage break down. He only did 1.66 mil to spore shooters on a kill attempt. In an 8 minute pull you have 5.3 mil. If your raid isn't killing shooters fast enough you are definatly on the right target and as there is no reliable cleave other then barrage, this usually results in a decrease in dps. Staying on the Fungal and Boss will typically lead to more dps cause it's more consistant cleave.
https://www.warcraftlogs.com/reports...ce=6&by=target
Where you could improve the most is abusing kill shot when your stacks are high. Take a look at the top parses.
The other difference you might notice is in the stack history of burning infusion. Compare this log to your guilds.
https://www.warcraftlogs.com/reports...ability=165223
You sadly enjoy more competition for the moss then similarly geared parses. In this particular instance his other throwers don't start taking stacks till later in the fight.
Other then that min max your movement for clearing moss as well as toggling your thrower smartly. Abuse your cleave and kill shots when your stacks are highest. If the boss is in range of moss do a big clear elsewhere and stand next to that moss to periodically refresh your stacks till you are required to stack for infesting.
Lastly don't switch off the spore shooters just to cleave to get prettier numbers if that is where your damage is needed. If your group is getting tank deaths, you'll most likely need to spend more time on the fungal. Remember you are not playing warcraftlogs, your playing world of warcraft.