I think that the weight of vintage Gibsons is what makes them the guitars they are.
Gibsons are known for their sustain and I think that sustain, in large part, comes from their mass.
My Epi LP Custom was manufactured in the style of the original LP Custom; all mahogany body, mahogany neck and I said it weighs about 10 lbs. but that's just a guess -- it could be heavier but whatever it really weighs, it's the sustain that blows me away. I swear that I could pluck a note and then go make a sandwich and it would still be ringing when I got back.
I think heavy guitars do that better and ultimately sound better.
When I bought my Fender Deluxe Strat, I intentionally looked for one with some weight and mine weighs a little shy of 9lbs and even unplugged that thing has some ring to it! My PRS has some heft to it and weighs in at a little over 7 lbs. and again I looked for one as heavy as I could find and just like my Fender, I can noodle with it unplugged and still hear every note, chord and bend and they all have great hang-time.
Heavy guitars also seem to have some very subtle overtones that lightweight guitars don't seem to have (or have as much) and that's yet another reason why I tend to favor them.
I understand why many manufacturers went in the "weight-relief" direction -- particularly Gibson because many people want a Les Paul but aren't too keen about having an anvil hanging off their shoulder -- but I also think some tone was sacrificed in the process. In the case of a Gibson (or Epi) Les Paul, if it isn't heavy then it just isn't a Les Paul.
Their weight is just part of their DNA.
To me, a lightweight guitar feels more like a toy than a real instrument and I'm sure I'm not the only one who feels that way.
I'm not a "tonewood" person and I know that the pickups, the amp and pedals all contribute to making a "sound", but there's something about mass that seems to make that sound even better.
I dunno.
Maybe I'm right or maybe I'm just nuts, but that's my opinion, for what it's worth.
Cheers!