in most cases the cage bar is closer to your head and harder than most things listed, and properly has no give. steering columns are by design & law collapsible, steering wheels flex. dashes also give, etc. you are probably not hitting a windshield with a OE belt unless it fails, but glass gives too. The cage steel does not give at all.
I'm not sure of the best way to describe it or if this will come out good in text, but I'll try. Hitting a roll cage would be more a more concentrated hit. You hit a flat surface with a tiny bit of give you spread out the energy/impact. I'm at a loss for a really good analogy, but I guess would you rather smash my head into the flat part of some 3/4" plywood than the side. both will hurt. I suspect one hurts much more.
No old (I mean more than say 10 years) car is much great at side impacts. That is the reason for the proliferation of side impact airbags. But adding steel closer to your head can't be good for an unhelmeted, un-hans deviced head. And in a cage it's the bar that runs high front to back that worries me most. And if a car needs halo bars at a given power level, well, that is race only. Again we saw that happen not too long ago.
It's not the 135mph crash you need to worry about on the street. You can never be protected from every possibility. Using outlier examples to support an opinion is illogical. If your example changes one key point - distance to the head - you no longer have a valid comparison. You need to be protected from the 80% of things that do happen. It's getting t-boned by a 18 year old girl reading a text that runs a rad light at 30 mph. If you get hit on the passenger side you should walk out. With a cage you might not. I've seen guys locally driving cars with cages that I would not get in because of that scenario.
I'll add this personal note too. I had my car on the track at NJMSP. I had it up to at least 125. No problems, everything went great, I wanted to do it all day, and started planning for other track events in the future. I plan on adding a little more power soon that would make 140 in the same spot easily attainable. My car has no cage or even a bar. But the more I think about it, and the more I talk to smart people, the more I realize either it gets a cage and becomes a race car or I cannot be on those tracks. All I need is a rad hose to pop or the guy in front of me to oil the corner and my family is in trouble. And I know I am not alone in that reassesment as it was the talk at Optima. Street cars with more power than winston cup cars and drivers with far less ability = something bad is going to happen soon. The guys that ran the track event I went to are now revamping their series because they have the same thought process. So I get the whole crossroads decision. I'm just glad I have not had the time & money to overbuild my car without thinking it through to the end. Which I did not. I saw what 'other guys were doing' and felt I'd be ok. I was wrong.
I spent a good 30 minutes talking to Ron Sutton while I was at SEMA. He is a well respected long time professional race car builder. He confirmed and added to my fears, for good reason. He has just begun a safety series at
Pro Touring and Lateral-G that so far I have found rather educational.
Last point to further muck it up. If you plan to insure your car for what it is worth using collectors insurance, etc., a bar or cage will greatly reduce the number of carriers that will cover you. For instance Hagerty will not.
Sure it will never happen to you. But we know a local family it happened to, not a made up scenario to scare you.