I think that Rosberg will be able to match Hamilton over the course of a season; Rosberg is an incredibly strong driver that is often underestimated, I, myself underestimated him before he joined Mercedes and showed a seven time world champion the way to go. It's unfair to claim that Rosberg will fall by the wayside when Hamilton gets settled into the Mercedes team!
I do not think he will fall by the wayside in any significant manner. I dont think he will get lapped by Lewis at any point for example. But I think Lewis will extract just that bit more performance from the car more often. Therefore he will tend to quali higher and do better on Sunday. Nico will be close or match him when things are good with the car etc. But when the car and circumstances are a bit more challenging I believe Lewis will be more consistent.
For example Nico has grabbed pole when the Mercs are clearly ahead, whereas Lewis has outqualified him when they were not as clearly ahead of the rest. Also Nico goes missing lot in races and I have yet to see him carve through the field like Lewis.
Finally when Nico has beaten Lewis in quali, it has been fractional, whereas when Lewis has beaten Nico we are starting to see the type of 0.47 difference thats mighty significant
So Nico is settled, and Lewis is settling and the pattern suggests Lewis is starting to extract more consistently out of the package