The unpopular Rammus opinion
At gold+ levels of ranked play, Rammus broke a 50% win rate somewhere between August or September 2015. This holds true at Platinum+ levels of play, and has only dropped twice at Diamond+ levels of play twice before immediately spiking back up. This would be two whole months before the Marksman update.
Somewhere along the way, Rammus got strong independent of Marksmen getting powerful. Any nerfs to Rammus right now are from an at least somewhat objective balance standpoint on a champion that is too strong, and is not a knee-jerk reaction from Riot for the community finding a champion that happens to counter Marksmen.