Here are the Mets ranks in four notable offensive categories by position as play begins on June 6:

Here are the league averages in those categories by position through June 5:

The Mets outfield has been generally unproductive all year long. Only the team’s right fielders have approached the league average in on-base percentage for that position, but every other category – specifically from Juan Lagares and the other center fielders – have not been good. The scary part is, outside of maybe Lagares, everyone else has been healthy all year long.
Couple that with the below average defense, and it’s fair to argue the area which needs the most improvement is in the outfield.
There’s not much they can do short of perhaps using Curtis Granderson in a platoon with John Mayberry Jr., or platoon Granderson with Michael Cuddyer and possibly acquiring a switch hitting corner outfielder (hello, Ben Zobrist?).
Either way, they need an injection of offense, not just in the outfield but the lineup as a whole. They cannot possibly last at the top of the standings with the group they have here.