1. Knife blink is pretty much the only thing zm can use against jet pack, plus since zm have knockback they also many times need that to get close to humans in the first place. Since zm are still quite a lot weaker then humans there is no point in limiting them further.
2. The limit for inf bombs is 6 which is not too much especially if you consider what I said previously about zm being weaker anyway.
3. Don't the see the point in giving extra damage to admins or similar that's what VIP is for.
jetpacks price is fine considering you get both a 500 damage extra, plus the ability