I'm not sure what you guys think a 4th/5th WR is supposed to produce.
Yeah, Meachem only caught 16 passes for 320 yards and 2 TDs but that's about what any team expects from a bottom of the depth chart WR. Meachem was also an asset pulling safties and blocking.
Whoever the 4th/5th WRs end up being, don't expect a 500-600 yard season from them. Morgan would be the exception because he's such a deep threat.