There was a lot more to that deal than just Clarkson and the draft picks. In fact it was a terrible deal but also remember the $3MM now was closer to $10MM two seasons ago.This goes back to the Malahkhov precedent, and the Rangers used this in the Zibanajed deal. In actual salary, the Rangers paid an additional $2M on Brassard, saving the Sens money. 2nd rounders are for $2M in salary, and that's the reason why the Rangers got an extra 2nd round pick in the Zibanajad deal.
CLB ponied up a 1st and a 2nd to Vegas to take on Clarkson. Clarkson is owed $3 & change in real dollars this year, thus the 1st.