Sorry to read of your great loss, exacerbated by rescue efforts that didn't go smoothly, leaving room for 'what if?' questions to haunt you.
Part of your post has content that deserves unpacking and clarification:
So lessons that I learned:
I will no longer dive with divers older than 55
I will no longer dive with divers that are overweight.
and
This is a repeat of many stories here on this forum of divers thinking that they are still ok to dive even when the risks are mounted against them.
You're an individual who's survived a traumatic event, and if you as a matter of personal choice aren't comfortable with diving buddied with or having on your own boat divers of a particular age, weight, asthmatics, diabetics, red heads, green-eyed divers, people who look 'soft' instead of bearing visibly defined musculature, people with dive pro. or tec. diving credentials not 'just' recreational cert.s, people with > 500 dives, etc..., that's your choice.
If you're implying people overweight and/or > 55 years old shouldn't dive (or maybe be allowed to? You didn't say that, nor am I claiming you did), that's another concern. Thus I'm asking for clarification.
Lots of overweight and/or 55+ divers dive, have a good time and go home safe. Every last person who does not dive eventually dies somewhere doing something besides diving. I get that the circumstances of scuba make some medical crises much less survivable than being at home, so life span may be cut short. I also get that older people drive 70+ mph on busy interstates, swim in pools and otherwise do things where a heart attack or stroke would be riskier.
Per your Dad's profile, he had between 500 and 999 dives, dove a range of destinations including all the Great Lakes and had Rescue Diver certification. While he rarely saw a doctor, on some level I'd think he knew his age and weight put him at some risk. And he chose to take those risks and do something he loved...scuba diving.
If this exact scenario happened to someone else and were reported here, and he were still with us and came upon this thread...I wonder what he'd say?