The 2009 playoffs offense sample size was three games. Bay didn't help with a .489 OPS (1 for 8 with three walks, the one being a single)
As for Beltre, how about mentioning that before he had shoulder and testicle issues last year, he hit at least 25 homers three years in a row in one of the most righty-power suppressing stadiums in MLB, the diminishing games played year-to-year were a direct result of the shoulder injury that ended up requiring surgery to remove bone spurs. Also, if you use OPS+ (which accounts for stadium factors) Beltre and Lowell have been virtually the same performer over the last four years, and you also forgot about Scutaro, who's an upgrade all things being said.
About Lowell:
Spot for Lowell will emerge.
Epstein says he might stay with the ballclub depending on what happens.