The guy is full of it. First of all, 1/4" of fiberglass would result in a canoe that weighed at least 200-250 lbs. If you did it with woven cloth (the most weight efficient means of generating strength, yielding the best fiber-to-resin ratio) it would take about ten-fifteen layers of fabric to generate that kind of thickness. No one who knows what they are doing would ever consider adding that much and a rank amateur would get bored and quit adding layers long before getting it that thick. If this guy isn't aware of the use of heat to soften and help remove both polyester and epoxy fiberglass, you can pretty much stick him in the rank amateur category, despite his "vast" experience... (a Lightning, by the way, is a 19', flat-sided plywood sailboat and there are tons of very badly "restored" Lightnings out there).
I have actually removed fiberglass from a canoe with a disk grinder, back in the dark ages (1975) before information sources like this one were available. I'm pretty good with a big disk grinder from my early days of using them to build strippers, but sanding a rib and plank hull is very different. In general, the tack heads survive OK, but what does happen is that just as soon as you cut through the hard fiberglass layers, the disk digs a dent or flat spot in the soft cedar. You end up with a boat covered in small dents and flat spots - all over the planking. This is already happening where he started sanding the hull and you can clearly see it in a couple of the photos. Unless you're willing to then cut away about half of your planking thickness with a long-board to get back to a fair shape, you're going to have a very lumpy hull. The only decent way to deal with the lumps are to replace planks or fill and fair the entire hull.
There is no reason on earth that this hull couldn't be stripped properly with the heat-gun method if somebody really wanted to put in the work required to do the job and thought it was worth doing, but you can bet your ass that the area he's already attacked is going to need to be fixed.
