I think you overestimate what Jet can effectively do in this situation. Ozai is letting Jet live at all out of affection for Lu Ten; if Jet went too hard against Ozai, he would just be killed. The only way Jet is going to effectively fight Ozai is to be subtle, and I don't think Jet can do that kind of subtlety. Especially in this situation where he has no allies whatsoever.

Jet's a decent guerrilla leader and a skilled combatant, but this is really not a situation where either of those skillsets is useful.

Also, he's ten years old.