The writer of Tali's story recently posted something along the lines of "tali is not a good combat leader."
http://forums.penny-...-toaster-today/It's buried somewhere in there.
But I think the relationship between Tali and Prazza is less than clear. If Tali is CO, then Prazza's action (defying his CO's direct orders in the presence of Cerberus) is simply unforgivable. It's one thing to say that Tali can't handle a group of well-trained marine, another to say that she can't manage a bunch of guys who hardly have any military discipline.
Tali's situation on Haestrom is better in some ways since Kal'Reegar appears to be following her command. However, it's also much worse since geth has superior firepower. 12 regular marines are simply not enough.
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about the Jack situation--WTF? This truly makes no sense. Being a teacher, even just a sports coach, requires discipline that I just can't see in Jack. On the other hand, showing off her abilities and beating other people in "practice matches" is something I can see Jack doing. Also, in the game, when you push a button and tell Jack to go somewhere, she usually does, so maybe there's the discipline that I was looking for.
I would think Jack was more suited to lead a biotic death squad which hunts down Cerberus operatives.