I sure wish I could find the interview, because I saw a great video on this five or so years ago and it kind of settled this issue once and for all for me.
It was a couple of Gibson engineers from the '70s talking about how difficult it was to get decent wood..
So Gibson actually did the analysis at the time and realized that the heavy dense wood at the bottom of a giant mahogany tree didn't resonate well. As some have mentioned before, there's some frequencies you want to reinforce and some you want absorbed and the heavy trunks pretty much transferred everything directly to the pickups because nothing was resonating at all.
Their answer was to source new mahogany tops but of course there were a heck of a lot of '70s Gibsons made out of the extremely heavy stuff.
The interview also talked about weight relief. At the time, they went the other direction and found good wood, but they discussed the fact that strategically placed chambers can definitely add resonance and reduce weight, they just didn't have to go that direction at the time.
I think this is definitely one of the answers.. if you've ever played the Revstars that are very strategically chambered, it's hard to beat the lightweight, incredible sustain and great beef in that design.
And I have played some very hefty 10 to 12 lb LP's over the years. I think they all had sustain, but none of them had tone that I would write home about.
As always, they're bound to be exceptions to the rules!