How many tanks are there? I mean, Bjørgen's a given. Assume Kowa is a tank too. Randall more than likely. Where is the line? Kalla's very muscular but nothing on Bjørgen and I don't really think of her as racing like a powerhouse in the same way as Bjørgen destroying people, or Kowa just grinding through with pure power and sometimes quite stiff and less aesthetic technique...
I always thought Skofterud was a real powerhouse but she's now doing really well in the real long-distance races
I don't think any of the current crop of Finnish girls are real powerhouse types, nor Weng, Falla, Østberg, and obviously Johaug. Steira I usually use as the counterexample to the likes of Randall when I'm complaining about the lack of balance in the World Cup calendar, because Steira to me is a good example of a proper skier. Yet some of the sprint specialists aren't the big tanks you might expect.
Really the "tanks" are very few in number, just they happen to contain the freakishly successful ones.