When I made the guide, the original soldering was perfect, as you'd expect in most manufacturing. It was my soldering that was not as clean as the original. The switches in the M65 that are stamped D2FC-F-K(50M) are definitely the point of failure. As to other mice, each can be manufactured with any number of other switches. In fact, in the M65 itself the switches on the side of the mouse for M4, M5, and M6 are different switches. They are Kailh switches instead of Chinese Omrons.
You can find a healthy amount of information about the particular D2FC-F-K(50M) switch itself as a particularly bad component if you take the time. That is ultimately why I ended up making the guide so that others could replace their switches if they chose to do so.