I have a question referring to the external auditory canal. Is the convex bending of the auditory canal usually strong enough, that any object (like a water jet or something) can not directly hit the eardrum?
No, at least not reliably. Each person is different and some tympanic membranes are situated in a pretty direct angle. Even in canals with a steep angle, a strong enough jet just ricocheting off the wall can still generate enough force to be harmful. Don't use any water jet type of thing that was not designed for ears. Some of the dangers are discussed in this article on cerumen removal: https://emedicine.medscape.com/article/1413546-overview