For Mutual Destruction, you don't even roll dice, just compare the printed attack value of all ships...
No, they've just ordered their sentences really poorly. "each player adds together the printed, unmodified primary weapon value of all ships in his or her squad" is clearly meant to be an alternative to "each player adds together the printed, unmodified primary weapon value of his or her remaining, undestroyed ships"
OK, well if that's what they meant, it is indeed very poorly written and unclear... especially since it's so easy to just add "..., then each player rolls that combined number of dice" or something to that effect.