Yeah, Stamkos isn't the guy you want moving with the puck. His decision making is below average. You want him touching the puck long enough to fire, and then he will score goals even at times when it seems like he can't.
In TB though, it was really good for Stamkos when Point became just as big, if not a bigger, threat to score on the PP. Teams had to defend the play to Point, which often left Stamkos open. You might see Nashville wind up with a similar structure. I feel like Marchessault shoots right? Maybe the plan is to stick him in the bumper spot, thus giving Forsberg and Josi more options. Seems like you might wind up with similar weapons to TB, if that's the case.
5v5 Stamkos will... well, disappoint. But if you put him in a favorable position on the PP, he will score. I think his 5v5 scoring will decline a bit, especially as you find better options, but I would imagine he will be a threat on the PP as long as he's in that spot. Ovy Lite.