I totally agree with that statement. We grew SM for two years, and they were always the first to get hit with disease. When they did produce they had very good tasting fruit, but because their poor DR, I took them out of our rotation. Their habit is very dense and bushy, so that may have been an important factor.
Regarding the wispy habit, I have grown a few Russian varieties, like Siberian Pink and Korol Sibiri, and they had a very wispy, frail looking growth to them, but produced fine. Pertaining to what @Drew51 mentioned, they are both oxheart varieties.