We got this down with 658 ilvl. Double hunter boom kin on flamethrowers.
https://www.warcraftlogs.com/reports/KdBpYZMzHfJ8NFnb
They were entirely responsible for spore shooters, everyone else did the fat add/boss.
Green mushroom should be healed to full only when infesting spores stars and let it die immediately after the Infesting spores debuff drops off.
Blue mushroom should be 100% priority and receive all external CDs. Tanks don't need them.
Healers should dps in spare time (no blue, no spores) but with 672ilvl dps check is trivial so shouldn't need to have them do that.
I think we used 1 cd per spores. Revival or tranq or barrier etc.