it could be argued but then again you could argue that I'm actually the King of England. there is no question a private space would be better, and cameras or bystanders won't do jack for you until after the attack has started.
Or staff. Even if they are super efficient they 1) will never be there when the attack starts 2) will most probably not risk their own safety if the attack is violent 3) will call the police at the next station, since it doesn't make sense stopping the train in the middle of nothing.
The best way of being safe is to avoid attacks in the first place. Being in a locked, enclose space (where you and you only control the lock) is much safer than being in a public space that anybody can occupy.