I imagine Grabber required more time to feed properly, like some I had especially my ghost Bandit, so it is easier to get more attached to them. Grabber surviving to old age with one raptor arm shows he was well taken care of, and kept fighting to survive. I would venture a guess he liked interaction with you as well, as he likely got attached to you too from the time spent and feedings - even if he didn't realize it at human relatable level (I think they do better than we give them credit for though).
I've only seen one mantid with a missing raptor arm (where the break healed from a previous molt) in the wild from the many hundreds of mantids I've collected or interacted with. So it is a health problem that appears to be fatal to nearly all mantids without a caring person feeding them.
I'm glad you both a special relationship, enjoyed your time together, and I'm sorry to hear he passed.
