I read through all of it and actually understand what you're saying.
Basically you're saying that drones are used to make spines and spores, but other races have defenses for both air AND ground without having to do permanent economic damage to themselves. While this is true, if you look at that in isolation it looks imbalanced, but its much more balanced than you'd think due to the other mechanics of zerg.
Zerg can create a lot more workers than the other races with a lot more safety. Because of this, not only do you usually have the extra money you could be using on static defences, but you also can sacrifice some of your economy towards defences without it having a noticeable impact on your economy in the long run.
Another thing you don't take into consideration is how cost-effective spines and spores are. Eight zerglings take up 200 minerals and 4 larvae, two spines take up 300 minerals and 2 larvae. Test out the maximum amount of marines each can kill and you'll see that spines are actually more cost-effective than other possible earlygame defences. Spores are pretty essential to hold some timings themselves, and are yet again really cost effective when used correctly. I dont see how either is really underpowered.
In short, I think you're looking at it the wrong way, or just looking at a small part of zerg mechanics in isolation.
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