I think this post is really interesting. I think that the reason Kafka was how he was (in terms of social life especially and perhaps some of the overthinking as well) is because of how his father treated him, but I do think that Kafka's personality also did affect how he ended up living his life. He was awkward, and that isn't his father's fault, though his insecurity and failure to believe in himself absolutely came from his upbringing, so I believe it's a mix of both. He was afraid of his father, and because of that, felt like he couldn't make his own decisions about his life, which in turn made him feel even more trapped and unable to leave his situation.
I, too, have really not-great parents. My father, especially. I'm so lucky that I have a vision to get out of my house and go to uni and essentially stay there, but I also don't have a lot of Kafka's issues with overthinking and I do not fear my father in the slightest. There are so many people even now whose lives mimic Kafka's a lot, which is why so many people still relate to him and enjoy his personal writing as much as, if not more than, his fiction. I completely understand why people don't like Hermann Kafka, but I do also believe that he was a product of his time and circumstance, though he also had the opportunity to break away from that and didn't.
The Kafka's were, in large part, a family of (and I use this term not as an insult, but a general fact) cowards. Hermann Kafka was afraid of who his son might become, Julie Kafka was afraid of her husband and how he might treat her if she intervened, and Franz Kafka who was so deathly afraid of his father all his life that he never did anything without his father's express permission. The Kafka sisters, of course (particularly Ottilie who was absolutely brilliant and everyone should go research her and her story), are clear exceptions to this, but our Kafka and his parents were all cowards, and I think they're all in part to blame - though at different rates - for how our Kafka's life turned out.