I consider anything over 8 grains per pound as adequate. I personally like my arrows around 9 grains or just tad more per pound of bow weight. That gives me the best combination of speed and mass. A person may well be happy with 650 grains on a 45 pound bow, but to tell someone else that it's the only way to go is wrong. Somewhere you reach a point of diminishing returns...where you are not getting back the results for your input.
Bowhunters were shooting through elk, moose, deer and bear, long before this heavy arrow mindset came along. Jack Howard loved the 2114 alumninum with 125/140'ish grain broadheads. Jack put down lots of elk, bear, mulies, et al, with a lot of pass through shots. That arrow was just barely over 500 grains, and Jack shot bows in the 60 pound range.
The bottom line is what has worked in the past, and has worked well, is not now ineffective, or obsolete for some reason. It's okay to suggest, or give your opinion, but let it know that it is just that. One only needs to revisit the past to see what has been effective.
If a person is using 700 grain arrows on their 50 pound bow, and is accurate with them, then by all means they should stay with that. The next guy may prefer 450 grains out of that 50 pound bow, and they will kill game just as dead.
It's all about quality broadheads, perfect arrow flight, and hitting the vitals more than anything else.