Bigfish,
I'm mostly in your camp, except for a few thoughts.
In the beginning, Gerber 15" and 30" sprocketed cutters ruled the world! They were Tangential knife (motorized knife) cutters, well built, very reliable, and terribly expensive. This was PRE digital printer time. Sign makers cut 100's of different colored vinyl and made banners. Summa (Summagraphic) cutters jumped into this market in late 1990's with a reliable 30" and later 48" Tangential knife cutter. Like Gerber, it was well engineered, well built, very reliable and also pretty expensive. As the sign industry continued to grow, so too did the list of vinyl cutter manufacturers including Roland, Graphtec, Mimaki, Mutoh, Ioline, and eventually companies like GCC and Vicsign. ALL of these cutters employed Drag Knife (Trailing Knife) technology. In the early years drag knife technology was inferior to tangential knife technology; but, in time became quite competitive with Summa Tangential Knife technology to the point where Summa was forced to introduce their own Drag Knife cutters. The Japanese built cutters (Graphtec, Roland, Mimaki and Mutoh) evolved into well built, highly reliable and less expensive cutters. The cutter market flip flopped and Graphtec became the defacto choice for most American sign makers.
I suspect your source is correct in noting that Graphtec controls 40+% of today's wide format cutter market. On the other hand, I tend to believe Summa is well below but still controls second place in American sales. I believe it is actually a superior product but it is still priced way too high to effectively compete with Graphtec and others for what is mostly large format die-cutting.
For cutting heavier substrates like Prismatic Road Sign material or for cutting very small graphics, I still believe the Summa Tangential Knife cutter is the best.