I don't think I have heard this discussion before, but I think that they are incredibly cheap for a unit that doesn't have a CLEAR counter (ranged infantry works well enough, though). Massing them is extremely easy for cavalry which can run past forts/ops, bump and run, and raid somewhat efficiently.
I don't want to say they are OP, because then people will think it is on the level of French or Ottos, but I think they ARE slightly too cheap. Perhaps I am wrong, but these are 110 (or 105) resources? Their price should at least be comparable to that of Cossacks, I think.
The only thing that holds them back is the Dutch econ, which takes a while, but once it gets going, these are very strong, and especially cheap for a unit used in industrial and imperial age.
Actually, now I am having second thoughts, that perhaps it is just the UPness of Russia and Portugal that I usually play and Dutch are closer to average. Opinions anyway please.