He had a pretty strong game last night: 1 goal (game winner), 10 shot attempts, 5 shots on goal.
That said, what you're seeing is what Stamkos is and has been for several seasons. He's a finisher and sniper who just doesn't want to shoot the puck anymore for whatever reasons (injury-related or just a "I want to become a more complete player so I'll try to become a playmaker and two-way player" which he just is not, not yet). Let me tell you, it's super frustrating to watch. He still has one of the deadliest shot arsenals in the league, he is still quite the skater, he's still one of the fittest players in the game.
He has (had?) the ability to disappear and fly under the opponent's radar only to re-appear out of nowhere in an open spot. The opponents only realized it when the goal horn already sounded. He's best when the puck is on his blade for no longer than a second. Now he's trying to drive the play or do a nifty pass - and fails more often than not, unfortunately. Sorry Steve, you're not a Crosby or McDavid.
It's also no surprise that his numbers went down last season and at the beginning of this season as soon as Kucherov turned dead cold. They fed off of each other last season and formed one of the best duos in the league. Now they're trying to make the pretty plays all the time, always a pass too much, always a dangle more which results in puck fumbles and giveaways left and right. Once Coop broke them up (Stamkos is now with Point and Gourde, Kucherov is with Johnson and Palat to reform the once great Triplets line) they both look better.
While some of this is true, I think it's avoiding the reality that Stamkos isn't the same player, physically, that he used to be. His skillset, particularly his skating, has diminished significantly. Watch him start from a standstill. It's way below average for a 2018 forward. Last game, he struggled to get by Trevor Daley, who was skating backwards. It was a play where anybody on our team not named Killorn would have blown by him and been in the clear. But Stamkos no longer as that ability.