Jason Vargas is certainly a change of pace. The veteran left-hander was by no means lighting up the radar gun Thursday in his spring training debut with the Mets. The soft-tossing lefty topped out at 87 miles an hour in two innings pitched and had a curveball clock in at 70. Three days after Noah Syndergaard blistered the scoreboard radar gun, hitting 101 miles an hour, the contrast that the Mets are going to promote is clear. It’s hard not to wonder if a change of pace will be good enough to boost this rotation, or if the Mets should have instead pursued one of the other available free agents. A middling pitcher for most of his career (an ERA of 4.17 in 12 seasons), Vargas is coming off a career-high 18 wins in 2017. The Mets think they found a bargain in the 35-year-old, who had Tommy John surgery in 2015, signing him to a reasonable two-year, $16-million deal. After initially saying they weren’t going to add a starter, the team-friendly free agent market allowed them to pick up a starter they think provides some stability in a rotation that has been rocked by injuries the past two seasons, a second lefthander among power righthanders and ultimately a change of speed from the rest of their rotation. But on the day that Vargas made his first appearance in a Grapefruit League game this spring for the Mets, it wasn’t yet clear how effective that velocity contrast will be. Sandy Alderson worked this weird free agent market well. With teams seemingly unwilling to spend, he waited out the free agents until he got a very favorable deal with Jay Bruce for three years, $39 million. He landed Todd Frazier on the eve of spring training to a two-year, $17 million deal and brought in five-time All-Star Adrian Gonzalez as insurance for Dominic Smith on a no-risk deal that pays him the major league minimum. And Alderson was shrewdly waiting out the starting pitching market as well, getting Vargas, who they said was their top choice at that tier, after pitchers were in camps.