Re: Jack Murdock
1. Butter, grass-fed, organic, blahblah. Do you know what's in ketchup?
2. So much of Jack has been shaped by his autism and his dyscalculia, not just in terms of how he interacts with the world around him but how the world interacts with him. Iiii am going to also take out his dyscalculia as part of this scenario, too
He MAY have been raised by his maternal grandparents as Jonathan Donovan instead of being given up at age four, but his senses were just as much of a problem as his autism when it came to his grandparents trying to raise him. Hypersensitivity is a common trait of spectrum disorders so his powers and his autism are almost linked.
Had he been raised by his grandparents, Jonathan never would have known his father and would have been raised to hate Matt for what he did to Milla. As a result, it's likely that he would have grown up to hate superheroes in general and the whole culture of it, and become an advocate for survivors of superhero neglect. I see him as snippy and impatient, because his senses are still dialed up to 11 but he never had the communication classes and therapy that encouraged listening skills and patience. He'd have few friends and prefer to be alone in peace and quiet, and take a lot of pills for constant headaches. He would never really understand his powers or be able to use them to his advantage, and always find them overwhelming - but he wouldn't be able to get his hands on a power dampener because he wouldn't have the right contacts.
Had he been abandoned by his grandparents for his overactive senses and sent to live with Matt, Matt would have trained him to work with his senses. I don't think their relationship would have changed much, but it's likely that Matt wouldn't have felt the need to be quite as protective or involved in making sure Jack had everything he needed. I think it would have taken him longer to retire from being Daredevil. I think he would have married Kirsten and maybe had other children. Jack probably wouldn't have had his interest in dogs and wouldn't have gone into education - he most likely would have gone into law like his father and stepmother and godfather. He still would have become Silent Knight but I don't think his identity would have remained so secret for so long, and he might have taken up the mantle of Daredevil instead and deliberately carried out his father's legacy.