Nelson immediately takes the top CB off of Cobb and makes a safety stay deep. But beyond those schematics or tactics, he simply would eliminate the need for 4 short passes by catching a 40 yarder at least once a game. Its probably not too far fetched to say Nelson adds one more threatened score every game.
But as you point out, teams with lesser receivers make their offense work. It should not be this tough to be competent.
Monty would help with all the man coverage because he is exactly like a NE slot receiver.