New Thornmail?

I've been playing a few games with the new Thornmail, and I have to say, I don't feel like it does anything for me as a tank. Personally, I've never been a fan of Cold Steel because its impact is really hard to see during the game and I feel like it doesn't line up well with Thornmail's apparent identity. The new changes seem to be pushing its viability as an earlier game buy but that seems odd because ADCs and the people you'd generally build Thornmail against are late-game oriented champions. So in exchange for late-game power, they've shifted Thornmail towards a mid-game item that falls off sharply into the late-game.

The addition of Grievous Wounds (GW) is certainly an interesting idea for Thornmail, but a simple calculation reveals that in exchange for Grievous Wounds, Thornmail is losing a ton of damage.

We'll assume the following: You possess 300 armor, 200 of which is bonus armor, when you're auto'ed you receive 1000 pre-mitigated damage, the ADCs lifesteal is 40%, and their magic resist is 50. We'll assume that the ADC possesses no armor penetration.

After damage mitigation, you receive 250 damage. Lifesteal applies on this portion of damage and if they don't have GW, they heal for 100 and 50 with Grievous Wounds. They also receive damage equal to 25 + 10% of bonus armor in magic damage with new Thornmail which adds up to be about 45 magic damage which is further reduced by their magic resist to about 30 damage. This means that with new Thornmail, they are healing for 20 per auto attack. Meanwhile, old Thornmail's damage was 25% of bonus armor + 15% of pre-mitigation damage which would come out to be 50 + 150 magic damage. This means that they'll be receiving about 133 damage which after lifesteal has been factored in, they'll be losing 33 health every attack. In the event the ADC has 35% bonus armor penetration, the damage they'd be dealing would be 300 which means they'd be healing for 120 normally and 60 with GW. With new Thornmail, they'd be healing 30 per hit and with the Old Thornmail, they'd still be receiving 13 damage per hit.

Damage wise, tanks lose out. However, the argument can be made that the utility provided by grievous wounds outweighs this damage loss. Yet even then, Grievous wounds lasts only a second so if the ADCs switch targets, they're fine again reasonably quick except in a few situations, the damage is just better. Still being able to heal while attacking a tank that is fully itemized against an ADC is a huge blow for tanks. Thornmail was rarely built before the change, but that's because it was so situational and provided tanks a way to survive and possibly kill ADCs but now, Thornmail has lost its ability to deal with a situational threat and become just another general purpose tank item with no real identity.