What would a pass to Ocho achieve that one to Welker, Gronk and Hernandez doesn't???
This is the point I think a lot of folks miss.
First, as long as the Big Three are catching 70% + of what Brady's throwing their way and posting beaucoup YAC and TDs, the #4 target (WR, RB, whatever) is going to pretty much be an afterthought. Doesn't matter if it's Ocho, Branch, Underwood, Edelman, Ridley, Woodhead, BGE, Faulk (who collectively have shared only about 25%-30% of Brady's targets) or . . . . Brandon Lloyd. It's not that they're "bad" (they aren't) or aren't getting open (they are), it's that the Big Three have been just so damn good.
Second, the Pats have averaged between 65-70 offensive snaps per game, 25-35 of which have been running plays. This leaves 35-40 passes per game, 25-30 of which have been targets to on or the other of the Big Three. Pretty much the only way Ocho, Branch or Lloyd (or any of the other potential targets) see more throws is if (A) Brady takes a target away from one of the Big Three, or (B) the Pats run the ball less.
So, it doesn't really matter if Ocho replaces Branch or Underwood replaces Och or Lloyd replaces Ocho - nothing is likely to change until some defense (or injury) provides a compelling tactical reason for Brady to target someone outside the Big Three.