Actually those were my initial thoughts too, but I think the complexity lost is not necessary complexity and there’s enough complexity in other aspects of the stage to fill in for that.
On the other hand though the more I think about it, I don’t think it would be a good idea to make oxygen and carbon dioxide passively absorbed. Instead I think it’s better if they are just made as large clouds that are quite dilute but common. This way glucose is typically the limiting factor to ATP production.
I think this would be cool because it would parallel the Aware Stage as well. Oxygen would be like water, a common resource that organisms need but don’t usually have to search too hard for, whereas glucose is like food, which is more something you need to hunt for. Sometimes though, oxygen (like water) will be rare or run out and then you’ll have to hunt for that, which could potentially be very dangerous with glucose levels being low.
On the topic of plants, even if carbon dioxide was common they would still be limited by the presence of light/heat spots and cells who hunt other cells (since plant cells would usually contain the most glucose). Plant cells would likely be hovering around light/heat spots, occasionally moving if the spot moves and occasionally facing predators attacking or shortages of carbon dioxide. This would also incentivize the cell wall (and by extension lack of motility organelles), because these cells would be usually parked in one place and wanting to have protection from attacking predators.
I’ll try to modify the mod’s values to make oxygen and carbon dioxide common and glucose and ammonia uncommon to show what I mean and we can see how it plays. Unfortunately I think the spawn rate of clouds is a universal variable though. I’ll check it out.