Rammus and his Dependence on the Enemy Team

As of the preseason, our okay-est champion has been doing fairly well in plat+. However, there are a couple essential flaws in the design of Rammus. But what is the flaw? Rammus still has a very anti-AD oriented playstyle.

"Why is this bad?", you may ask. I believe Ghostcrawler said it was one of Riot's core design philosophies that games should be decided by how you play rather than being decided at champ select. I believe Rammus's kit focusing completely on armor impedes his ability to deal with magic and thus makes the Rammus pick either effective or in effective based on the enemy's champion.

I personally would give Rammus's w an MR ratio (of course nerfing the base damage to make the change more or less power neutral) such that Rammus's main damage source is not punished while building MR. However, I'm not all too experienced with game balance, y'all at Riot should look over the problem to find a proper solution. Ok?