A few things come to mind with regards to this thread,
-You can kill things with far smaller guns than standard. It isn't always a good idea, I do it too when weight is a worry, but because it's been done by no means translates into the majority of average shots are overgunned.
-Not all Grizzlies are created equal, many are only half again bigger than black bears, die just as easily, but they do have a far more tenacious disposition and if they make the alders problems can turn into disasters quickly.
-The .25-20 nonsense is ridiculous, sure it's possible, but I haven't seen more than one bullet exit on coastal Grizzlies and that's up to .375 Ruger.
-In the good ole days wounding wasn't as much a concern, nor were modern ethics. Grizzlies were vermin in those times, and much different standards were accepted in their treatment.
-I struggle to believe MiG25's grandfather killed fifty, and just like the bible believe there is some underpinning of truth to a rather exaggerated set of stories. Unless MiG25 is having fun with us, I suspect even some photos may be in the family archives as many hunters in BC have killed Grizzlies, especially historically, often with guns not terribly well suited to the task. It's not an overly remarkable achievement here, and many hunters here have grandparents who've killed Grizzlies with .30-30s or .25-35s, and so what?
-The old timers were also no smarter than you. They were human, and while legend making is a fun hobby often the old timers were ill equipped, operated in times of far higher game numbers, with a much more casual take on shot selection and the risks of wounding.
In the end, I want to know what the OP's end argument and position is. If it's just to stir the conversation stew he's succeeded handily.