Sometimes, when they have not mount for a while or never, they are anxious, after the first time they may be less strong, never the less, you can manage to be mounted tring a couple of times, you will get used to the violence of penetration by time, i am not sure if this are your fist expiriences, later you will learn how to manage them.
My first dog who was a mixed one, was very gentle in a dog way and used to knoted me with autority i can say, it was easy to get knoted besides the violence, later i have two rotweillers, that for some reason, they are more anxions and rudes, with time a learned the manage them and behave them a little bit too, but still they are more restless i can say.
About being bitted in an aggresive way, i have not those expiriences, sometimes in a gentle way they have bite me my arm, in a way to ask me to get in possition to be mounted, i dont see the tring to damage his bitch, sometimes once knotted my second and third dog used to growl a little bit, but i consider it is for masculinity passion once knoted.
May be the owner that taugth him to be aggresive, mine are always family dogs
Hope this help you kisses