More than three weeks into a longer-than-normal spring training, all the giddy talk about the young arms, the Mets’ pitching future, is beginning to give way to the reality that the present starting rotation is full of uncertainty. And as a consequence, there is a sense that some Mets people are beginning to brace for the worst from the 2013 season. It’s only natural, with Johan Santana continuing to leave everyone guessing about when he’ll be ready to take the mound and what he has left in his arm. Not to mention free-agent pickup Shaun Marcum has the brass wondering why he’s hitting only 82-84 mph on the radar gun. Don’t forget, Dillon Gee is coming back from shoulder surgery, due to a blood clot, and even at his best he’s a No. 4-type starter. So even if Matt Harvey continues to takes steps toward being an ace, the wild card of sorts as it applies to Mets pitching, both present and future, is Jon Niese. Seeing Niese get smacked around for four runs and six hits in 21/3 innings on Wednesday by Team Venezuela wasn’t great for morale at Mets camp, but he was pitching against something of an All-Star lineup, and, of course, it is still March.