I wouldn't treat F1 and other open cockpit series as different in this regard. They have very similar risks regarding head injuries (of course the speed the car has also influences the risk, but the exposure to the risk is the same). What happened to Surtees could just as well have happened to a F1 driver, because both cars at the time had very similar exposure, while a Halo would have bounced the tyre off without putting pressure on the driver's neck.
Shrieker did make a good comment. Yes, Maria was really a freak accident and you can the truck being there with loading door open as a big contributor to it. However, your original statement is that it would not have saved anyone, while in Maria's case it would have. In massa's case it would have not helped of course (but, the new helmets and a cockpit individually would have).
Even if it did not help anyone in the past, are we really saying no to increased head protection? Yes, it can be described as ugly (although I can certainly come up with much better examples of ugly bodywork we all got used to eventually), yes they could have done a better job with aesthetics or have gone all the way with closed cockpit with an integrated halo. At the end of the day, if we want to combine high speed cars with risk reduction for drivers, we shouldn't play down the safety benefit.