well i think the future will tell how impressive Hamilton has been at Mercedes against Rosberg.
In a couple years if Rosberg gets teamed up with Ricciardo or Alonso or Vettel lets say and he just runs right through them then that would put Hamilton at the highest level.
If Ricciardo or any of the above decimates Rosberg then you can begin to question Hamilton´s abilities.
So far though we can say that Hamilton has had the upper hand on all teammates but one, with Alonso as a rookie.
If Rosberg actually won the title this year then Rosbergs stock would have been sky-high, considered to be the best driver in F1 arguably but he´s not done that, he´s just won 3 races after his teammate won his second title in a row.
People have short memory so Rosberg is in high regard right now but if you look over a 2 year span the only conclusion you´d come up with is that he´s lethal in qualifying.