Stamkos needs a guy to get those pucks on the boards and do the dirty work, like crashing around the net, throwing Callahan there will get that task done, Adding Drouin will get him that playmaker as well. We saw very little of Drouin - Stamkos - Callahan and it was good, they even scored a few goals together.
Unless we are going back to KFC which was a very good line, Cally stays put with Stamkos. Paquette was not great with Flip and Cally, and that line was too one way on the defense end and just very limited.
If Callahan was a LW, he'd be perfect. As a RW, it's probably never going to be optimal, nor our best option. Stamkos doesn't cycle the puck well enough to take advantage of Cally, and Cally doesn't pass off the rush well enough to take advantage of Stamkos.