If you have access to a gym, then lat pulldowns will help. If all you have is a chin up bar, get a stool or box that will bring your chin to the bar. Use this to do cheater pull ups. Stand on the box or stoll, then try to hold yourself up as you lift your feet. I’m going to be adding this to my workout after I’m unable to do proper pull ups so I get a full workout of the relevant muscle groups.

And by the way, doing pull ups is unlikely to ever be a life or death matter. Few people ever find themselves in a situation where they need it. The disasters mentioned were notable exception, but we are unlikely to find ourselves in such a situation. The ability to run fast is a survival skill you’re slighly more likely to need in your lifetime (plus it has other uses, like catching the ice cream truck).