Sort of a funny story....I agree. All you need to do is train that hook on a heavy bag, without any wraps or gloves or support or protection for the hands. With the horizontal fist, it is very easy to land with the last knuckles, and that risks injury. You can feel that potential on the bag, even if you don’t get injured.
Vertical fist is better. Avoids the injury much better. That is how you need to train it if you might need to use it outside the ring, without wraps and gloves.
I used to tournament fight when I was young. Tons of them. There was an EMT that worked the big tourneys, Ted, a great guy.
I went to him one day and said, "Hey, Ted, can you tape my hands?"
He said, "sure, two bucks." To this day he taped hands better than anyone else I've ever met.
People didn't tape their hands for point tournaments. But soon, everyone was coming up to me asking, "Hey, who taped your hands?"
I'd reply, "Teddy did, it's awesome, feel them." They would.
Within a month, and to this day, or so I'm told (because he's still at it) Teddy was taping everyone's hands. He made a ton of extra cash. And I'm glad. It I were hurt I'd rather have Ted taking care of me than any doctor I've ever met.