Hmmm...I would say that after almost a lifetime of examining, playing and making 19th century guitars that I cannot agree with much in that statement. I would also not take the statement from the curator of antique furniture as truth as it applies to musical instruments. I have nothing against antique furniture curators but I think the author has made an erroneous leap of logic in equating a guitar to a piece of furniture or even a violin/cello. The very nature of the guitar and the way it is built tends to give it a "best before" date which isn't necessarily applicable to violins, cellos, violas, or chairs.
I will conceed that many (certainly not all) 19th century guitar builders did tend to utilize thicker (could read "heavier") tops and often backs than modern builders would but to make this statement "... surviving 19th century guitars are often extremely difficult to play with fingertips. The choice is often between audibility and dexterity and even with one's best efforts, many surviving instruments (and modern copies) are so heavily built that playing them without nails feels, I imagine, like trying to eat steak with no teeth! ...." shows a complete lack of understanding of the principles of 19th century building IMO. Some of the loudest,and easiest playing instruments I know of were made in the 19th century.
I'm not sure why Mr. carter would make such a statement when it is clearly inaccurate to those who work with these instruments on a daily basis. Perhaps to advance the reputation of his friend, the guitar maker who made his instrument...It's puzzling...
However, after reading the full liner notes, where I suspect this excerpt came from, I see there are a number of bold statements which seem a little "over the top" and ill informed.
Scot Tremblay Guitars
"One picture is worth a thousand words. So, for me, one good note put where it should be put, will say what it will take some people many notes to say. ~B.B. King, 1986