I'm sure that less than second added a hundred times over can save some lives, plus in a tighter situation, bags behinds your back or in your hand will take up additional space that could accommodate another human.
I am pretty sure that except for the people adjacent to the emergency exits, the others will have to wait their turn for a much longer time.
A backpack carried on the breast would not occupy space in which another human could have stayed.
For life or death situations, you need to have short clear rules that are easy to follow.
Remember, you will only actually lose your stuff if the plane is destroyed. If the plane is in the middle of being destroyed, just get out and be glad you are still alive!
Looking at this thread, we might need to put into regulation that taking baggage during an emergency evacuation is criminally negligent. (If someone behind you dies, negligent homicide.)
Everything else takes a back seat to those priorities.
An individual backpack might not displace an individual human but across ~300 passengers those 50 backpacks will displace people.
A passenger has practically zero information as to the seriousness of the crash. It could be a doozy. Or there could be a fuel leak waiting to ignite.
> backpack carried on the breast would not occupy space in which another human could have stayed
You're claiming given two lines of people, one wearing backpacks, the other not, that the latter cannot be compressed more than the former?