I feel like at some point the fungus infection would have figured out the fact that it is insanely flammable and that one spark could completely eradicate its collective species in a course of hours.
I feel like there would be some kind of means of protection that supports the fungal bed. The fungal bed itself is basically one giant reproductive organ, yes? Spitting spores up? What about what’s underneath? I would think there is something below, something like a root system, or like the stem of an actual mushroom that exists below the ‘fungal bed’ tile.
In my head it looks something like this: fungaloids waddle their mushy selves around randomly and vomit spores sometimes. The spores will sometimes take root, and begin to grow a thin membrane across the ground. The membrane itself does nothing except grow and spread across the landscape; think a translucent veil made up of a spiderweb of vein-like fibers spreading slowly across everything it comes across. It slowly thickens as it gets wider and wider and meets up with other patches of membrane.
Once it’s big enough, the thickest part in the middle starts to grow advanced parts and reproductive bits, like those tendrils and the proper ‘fungal bed’ as we know it currently. Spores that root on the membrane becomes a fungal bed tile, and the growth of the fungus in that particular area starts to spread exponentially. The central part rapidly grows outwards to meet the edge of the membrane, which is expanding further and further to perpetuate the ecosystem.
The membrane itself is, of course, only slightly flammable. It’s moist and doesn’t burn very well, so you’d have to look into alternate means of getting rid of it (like big turbines or tracktors or something to rip it up). The fungal bed parts might be flammable but it would probably develop some kind of mucus-y self defense mechanism to help cut off potential wildfires to prevent the entire fungus from getting incinerated. Maybe this can come into play with the ‘raging fire’ tiles appear - sparks trigger the mucus reaction, not quick enough to extinguish burning tiles, but enough to contain the outbreaks that do happen in a radius around the source. Then once it’s extinguished the ecosystem can heal itself naturally over time.
This would also have the perk of balancing the fungus out early game, when it’s still generally spreading its roots out and preparing to support bigger and better fungus systems. Early game players are weak and don’t want to deal with anything bigger than fungaloids; once you hit late game, you can start to bring out some of the more monstrous fungus manifestations. The fungus is an aggressive slime mold invading the world, and sooner or later it’s going to develop something a little more mean than just little tendrils. There has to be a bigger threat to the fungus besides ruining farming, because players can just suit up in airtight suits n junk and they’re basically immune. The fungus needs some nasties at its centers. Something like antibodies.
This is what I would do if it was me. The fungus starts as something like its original species prior to the blob outbreak, but on a larger scale; its when we start to see the entire system come together that it starts to behave less like a mold and more like a gigantic entity spread out across an entire ecosystem. Entering a prospering fungus biome would be less like entering a forest as slipping under the skin of something very much alive. Because that’s what it is, right? The triffids are gardeners; the fungus is a slime mold. Whereas the triffids are plant people among trees, the fungus is just one big entity that gets progressively more and more complex.
That would ALSO support lore-wise why the Triffids don’t want the fungus to get any larger than can be contained: if it gets too big, you’re talking something that’s even too great for them to overtake, and becomes competition. Then suddenly they’re not so useful anymore.
Just some thoughts for someone to consider maybe. I can see some really huge things that can be done with the existing factions and why you might not want to leave them to their own resources forever. That or do some right and proper defense-building yourself, because it’s not your world anymore. Take it back or keep what you’ve got from being further taken from you.