Everybody thinks their own beard is tough :-)

As I see it, the problems with a heavier beard are threefold: (1) the thicker hairs are more difficult to soften all the way through (2) the tougher whiskers damage the edge more during the shave (3) even a little bit of degradation in the edge causes painful pulling.

This means that increases in beard toughness can have a very nonlinear effect on the shave difficulty, so slight increases in beard toughness can cause a much more difficult shave because all these different factors multiply each other.