Well, I don’t know. Because you can choose what to build as you mentioned you got 10 larvas and you can choose. 10 workers or 10 (20) lings. But you can go 50/50 while Terran yes have eco boost from mules but can’t trade it like ok lets drop marines instead of mules. They can kinda build just more barracks for these resources and get more marines instead of SCV’s so you are partially right there.
As I mentioned before that combination is extremely rare or like non existant. Zerg players usually build one a-move army and gives 1 spellcaster to it. Not all at once.
It still gives you the point of “choose” what to do. And when you gets better you know better how to spend energy and then the zerg is a serious threat to other races because they are immune early and mid when they scout properly and then destroy everything late game.