Is the mahogany on an 8 lb guitar the same wood as one on an 11 lb guitar? The densities are dissimilar obviously, so are they even the same sort of guitar?
I'll stir up some controversy. The first is the question as to why mahogany was used for the Gibson then Heritage solid bodies. Mahogany was an established tonewood for acoustic instruments, which makes sense. But why use it as a large slab for a body? I can't answer that fully but at least in part it had to do with furniture manufacturing, which was a big industry in Michigan in the last century. Mahogany was plentiful, relatively cheap, durable, and didn't fragment and splinter much when shaped. Those who argue that it was chosen for tone have to consider that there is really no history of Gibson experimenting much with other woods with the exception of the maple cap. Korina is fairly similar to mahogany in properties and never was a serious contender to displace mahogany as the default building material. http://legacy.gibson.com/News-Lifestyle/Features/en-us/korinawoodmakesgreatguitar.aspx
Gibson mahogany tended to be lighter in the 1950s. I don't know why that worked out that way. It could be the abundance of old growth, longer drying, harvesting from different regions, decreased shipping costs, or company preference for other reasons. As time went on, the weight tended to increase. Weight relief was a solution in part. Even in light guitars, like the Tele and the PRS SE 245, weight relief gained traction.
The early Heritage H-150s often were about 10 lbs. Some claimed that extra heft enhanced sustain and created "tone monsters". That term obviously means different things to different people. The original concept of the LP was a maple cap presumably to give high density for brightness and sustain when placed on the current source of mahogany that was lower density back then. More recently commercial mahogany is available with density similar to maple. That raises the question as to whether the maple cap is now more of a tradition or for appearance.
One thing for sure is that lighter mahogany weighs less! It is easier on the shoulders and backs.
Curiously, the LP Customs and some of the H-157s had no maple cap but had solid finishes. That suggests the maple cap was at least in part for appearance.
I am very familiar with the book Beauty of the Burst and the extensive discussions on wood harmonics and choices. Even if those discussions were true, there is less relevance today because the signal chain is very different in the 21st century.
Consider Fender for a moment. They used and use lighter wood and have an overall lighter guitar. Some say their popularity is due to a lower cost, which there is clearly merit to that. But it doesn't explain why Gibson couldn't compete with Fender with the Melody Maker and Les Paul Jr. back in the 1960s. Further, it can't account for the widespread use of Fenders among professionals, including in the fields of blues and rock. Here is a clip of Fender and Heritage. I personally like the sound of the Heritage better. But look at the audience. Is there a single disappointed face when Frankie plays the Fender? https://www.youtube.com/watch?v=XFtdEkG_OoI
Can the wood be too light? I was warned not to buy a G&L made of empress (paulownia) because of the low density and potential for screws to strip out. I got it anyway. It is very light, under 7 lbs. It has good sustain and seems durable. No regrets.
To summarize, solid body guitar players tend to like less heft to their guitars, which is understandable. They draw the line in many cases against weight relief but embrace low density to achieve lightness. Contrary to this summation is that thin necks are not uniformly embraced, so the added weight of a heavier neck is acceptable. Finally, the infinite possibilities of the signal chain won't offset the loss of "tone" in a guitar of improper density.
As I have discussions with engineers about the history of the structuring of electric guitars, it takes little time for them to ask enough questions to reach the conclusion that the tonequest is beyond physics and math and enters into the realm of aspirations, symbolisms, and intuitive beliefs. It is in this realm where passion stirs.
On a personal note, I have H-150/157s ranging from less than 8.5 lbs up to over 11 lbs. All of them are excellent. It is a buyer's market for the heavier guitars. The market does change. Consider that Gibson couldn't sell LPs at the beginning. Those same instruments are going for huge sums now. The original PAFs were literally taken to the dump in large numbers in the 1960s to make room for the latest and greatest pickups. Back when I would do three hour gigs, quite a while ago, I used a weight relieved guitar, a semi-hollow. No one would have ever thought that was bad guitar despite its overall low density. That would never entered the realm of possibility of discussion. That was a different time.
I apologize if any of this content is unsettling. I try to reflect the overlap of practical industry and marketing decisions at Gibson, and by consequence Heritage, with those instrument designers who did pursue tone as well as other aesthetics. The result wasn't the epitome of elegance (note the acrylic fretboard inlays), but was an excellent instrument that was reachable in cost to a large enough to be financially viable. Even with these compromises there were some failures among the many successes.