Idk, but either I'm underestimating danger or overestimating safety here. When Grosjean went into the barrier I didn't even think that he will die. Like at the moment I remembered the stuff that makes sure he won't die in this day and age, like halo, all of the fire-resistant layers, that marshalls these days are actually equipped to fight fires, the medical car behind the pack, ability to airlift drivers to the hospital and the carbon chassis that is built to take impacts (If Kubica didn't die in Canada 2007, Grosjean doesn't die here).
I guess it depends a little on how much racing stuff you have watched in the past. You watched the fatal crashes of many drivers, but was that only videos of those crashes on youtube or the live coverage, cause that might explain some of the difference (and also, you have more trust in F1 engineering and possibly a more optimistic take).
For me, I immediately thought that this was a really bad crash, that was very likely to be fatal for the driver. As you said, there are a lot of systems that give drivers a very good chance to survive and this crash would have been simply unsurvivable without Halo, Hans, the padding around the outside edge of the cockpit and so on.
However, the way how this panned out, especially on live coverage, had a lot of really bad signs:
- The car went straight off the track without losing any speed whatsoever and crashed directly into a naked steel barrier.
- It exploded into a huge ball of fire, something that I can't even remember ever seeing happen in a crash (the last time a car went up in flames that I can remember was Verstappen 1994's refueling incident). This explosion implied that the damage sustained by the car was way more severe than even the crash that took Hubert's life and that the car has broken in a way that has never been seen before with this kind of car and this set of safety features.
- The live coverage did not show the aftermath of the crash or a replay. That usually happens when something really bad happened, the driver is still not salvaged... and with the tank ripping open and spilling almost 200 litres of racing fuel all over the wreck... well. Doesn't take much imagination to figure out what that might spell out. When they did cut back to the scene of the accident, for a short moment, they showed an angle where you could see that the car was torn in half and the cockpit was just completely gone, thankfully, they immediately went back to show Grosjean in the medical car, so we knew he was alright.
There is also one thing regarding the Halo: It did save Grosjeans life, no doubt about that, but up to this crash, we didn't know the Halo was capable of even withstanding such a blow. It's meant to deflect wheel assemblies striking the car, the loads of having a 1 ton vehicle crash into a rigid steel barrier at speeds in excess of 150kph are an entirely different beast.
Kinda like back when they introduced the monocoque, no one knew how much it would actually withstand. I once saw a documentation, where an engineer of that era said that they weren't entirely sure how exactly it would crumble in case of an actual accident (not just a simulated crash test). Some engineers feared it might just crack open like an egg, but it turned out that it crumbles from the point of impact onwards, meaning that for every inch of monocoque that gets smashed into powder, the car loses absurd amounts of kinetic energy and that it is the most perfect system to ensure a driver's safety.
In this case, the Halo had to deal with an impact it was simply not designed to take and it somehow held together. I would not count on it working a second time in a similar situation.
Looking at the aftermath of the crash still gives me the chills. The torn off cockpit stuck in that fencing alone is nightmare fuel - even after the fire was extinguished.
How insanely lucky that the cockpit was torn off in one piece, there have been crashes in open-wheel racing where the cockpit broke open right along the edges of the back rest.
Something to keep in mind as well: Grosjean had the wherewithall to unbuckle and get out of there asap. He didn't lose his head or panic, that is pretty admirable.
When I saw the car in two pieces I did have some thoughts of the Hubert crash to be honest luckily it split in a different place.
Even with all those safety features had that car been at a slightly different angle he wasn't getting out past the barrier or if he was knocked unconscious and wasn't able to get out himself it would have been a lot worse as they would not have been able to do that until that fire was out.
A lot of the times, it's not even the burns that kill the drivers, it's the fumes that they breathe in and the lung damage that this causes. Not only are the fumes highly toxic, but they also boil your lungs from the inside. Lauda sustained severe burns on several parts of his body, but what almost killed him was the toxic shock and the lung-damage. Even if they had managed to douse an unconcious Gorsjean with extinguisher fluid, chances still are high that he'd breathe in enough toxic stuff to suffere severely.
Edit:
Compilation of all driver's reactions to Grosjeans crash.