Equivalent Average (EqA) is a creation of Clay Davenport over at Baseball Prospectus. I highly recommend him.
EqA is a rate stat designed to measure everything a player does in his team's half of the inning. It's normalised to a scale designed to mimic batting average so as to provide a familiar range of scores. As such, the league average EqA is always .260
The Mariners aren't doing so hot. Minimum 50 PA:
.268 Willie Bloomquist
.267 Raul Ibanez
.267 Carl Everett
.266 Ichiro
.263 Jose Lopez
.259 Kenji Johjima
.251 Yuniesky Betancourt
.249 Adrian Beltre
.245 Jeremy Reed
.244 Richie Sexson
The upside is that only a few of those guys are hitting as well as can be reasonably expected. Lopez, Everett, maybe Ibanez. Betancourt. Everyone else is underperforming. Either something's wrong with them, or they'll improve.
Just for fun, let's compare them to the Jays' EqA numbers - same parameters:
.298 Frank Catalanotto
.294 Vernon Wells
.294 Alexis Rios
.293 Reed Johnson
.285 Greg Zaun
.282 Troy Glaus
.280 Shea Hillenbrand
.274 Lyle Overbay
.271 Eric Hinske
.259 Bengie Molina
.253 Russ Adams
.237 John McDonald
.231 Aaron Hill
First of all, that left field platoon is sick. The only other team getting production like that out of LF, a premium offensive position, is Milwaukee with Carlos Lee. And, there are NINE GUYS performing at a higher rate-based level than anyone on the Mariners. Anyone. Even freaking Eric Hinske (admittedly in a platoon protecting him from lefties) is outperforming all Mariners.
The real story here is that the Mariners can't hit, even worse than anyone thought they wouldn't be able to hit. But those Jays are tending fairly strongly in the other direction.