"Thornmail" inspired concept for a Rammus tweak

Okay- so before we all start talking about me being a Rammus main trying to flex my champion: consider I made my account before his rework.

I consider the Rammus rework to be a nerf. I will say this: I do understand the implications of the rework. Being allowed to just show face and harass AD champs with no consequence is a bit easy OP. (even though it was fun watching champs like Jinx melt face in 2 seconds)

But I think the whole slow is a bit much. The first time I played the rework (I didn't read patch notes at the time like a noob) I was wondering who had a Nasus. It literally feels like Wither just draining the hell out of you. Especially when you know Rammus as a high-mobility champion.

This is my suggestion: Considering Rammus has no passive effects to his abilities, and inspired by the "new" buildpath for Thornmail using the Bramble Vest: Can we consider a passive on Defensive Ball Curl that reflects base magic damage to attackers? Before we say that would be OP- hear me out.

The damage directed this way doesn't need to scale off anything, much like Bramble Vest, and can be minuscule enough to actually be viable.

Defensive Ball Curl passive: Attackers take (4/8/12/16/20) Magic Damage active: Rammus drops into a defensive stance for 6 seconds, gaining bonus armor and bonus magic resistance, increasing Spiked Shell's damage by 50%, and applying it to enemies whenever they use basic attacks against him. Rammus is slowed by 30% for the duration.

bonus armor: 20 + (50/60/70/80/90)% total Armor (current state) bonus magic resist: 10 + (25/30/35/40/45)% total Magic Resist (current state)