Tying a dog may or may not make it aggressive- depends on how it is done. If a dog is tied up and neglected then I imagine you are right. If a dog is tied only when the owner cannot directly supervise it and is off the tether most of the time it won’t be aggressive at all. Tying a dog up or kenneling a dog or keeping it any other way are not bad- of course like everything else a bad owner can make it bad.
If off the tether most of the time, sure, it won’t be aggressive; but, based on my observation, if it’s on it most of the time it definitely will be. So we agree.