Red Sox fans playing the gleeful what-if game in the wake of Alex Rodriguez’ latest PED allegations — “Thank God we didn’t get him!” — actually have a more relevant Yankees target to consider. Yes, the Sox almost signed Rodriguez in 2003, but let’s be realistic: He probably would have posted monster numbers before opting out in 2005, at which point the Yankees might have signed him for $275 million anyway. The player the Sox should really be thankful the Yankees swiped away is Mark Teixeira, who has served as a knee-jerk example of meddlesome Red Sox ownership screwing up a done deal, when in actuality he never should have been pursued in the first place. At the time, the Red Sox were ripped for failing to go the extra mile. They came up roughly $8 million short and watched Teixeira sign with the Yankees for eight years and $180 million. Many continued hammering John Henry and Co. for letting him slip away as recently as this season, when Adrian Gonzalez, the man acquired as a consolation prize to Teixeira, struggled before being shipped to the Dodgers. But in case anyone missed it, Teixeira has experienced a steady decline since his first day in pinstripes, a fact he acknowledged in a thoughtful, candid interview with the Wall Street Journal during the weekend. “I looked at the first six or seven years of my career, I was in my 20s, it was easy,” Teixeira said. “I wasn’t searching for the right formula. To think that I’m going to get remarkably better as I get older and (break) down a little bit more, it’s not going to happen.” The numbers support that assessment. Since blasting 39 homers and finishing second in the MVP voting en route to a World Series title in his Yankees debut in 2009, Teixeira’s numbers have dropped. He still has averaged 32 homers a year since 2010, but his average has fallen to .252 in that span, with his OPS decreasing in each of the past six seasons, from .963 in 2007 to .807 last year.