I don't believe it was ever supposed to be a reliable source of damage to allow tanks to theoretically win 1v1's against carries. Its past self either didn't serve its purpose, or did it too well in cases like 
or 
. The new one, even if the damage has been toned down, serves what I believe its intended purpose is as being a solid deterrent for focusing tanks, hence the addition of grievous wounds in a sustain-heavy meta.
Just my 2c
I WANT MY THORNMAIL TO ONE SHOT PPL !!! http://i.imgur.com/Q3z4Ix6.jpg?1http://i.imgur.com/Q3z4Ix6.jpg?1
They're comparing it to season 4 and earlier Thornmail where adcs would literally kill themselves by autoing a tank. The fact that was ever in the game was a load of nonsense.
{quoted} serves what I believe its intended purpose is as being a solid deterrent for focusing tanks
But taking a whole bunch of damage for hitting the tank isn't a solid deterrent?
Thornmail was a weak item, and this patch made it worse (at LEAST for tank).
The crap part about thornmail is how it now lacks synergy with other armor items and even has some overlap with randuins which isn't ideal
i would rather lose the AS slow in favor of a better armor scaling tbh
I often buy it as my only defensive item these days because it does everything anyway and building more armor items won't really make thorns passive better anyway
getting randuins alongside it is now only worth it when they are like full ad and they have like 2+ crit users
Frozen hearth might seem like a good option since the AS slow wont overlap but stack, but there is a caveat, the lower attackspeed messes with the 1 second grievous wound application making that part worse
So the synergy with the 2 other heavy armor options is just bad
15% physical AA damage before mitigation (+25% bonus armor) vs. 25 flat (+10% bonus armor)
That's a massive reduction in damage. Even if the Grievous Wounds was worth it, the reflect may as well not even exist.
It was supposed to reflect damage because ranged champs with lifesteal can use a tank as a healer. However, anything over 10% lifesteal negates old thronmail.
Really the item is a bit of a mess. Get the vest and spend your gold else where. The damage reduction is massive, meaning adcs can still drain off you, just a little less.
You have no idea how salty I was when my build didn't even slightly deter Ashe from dealing 50% of my health during teamfights and staying topped off with an overshield.
I do agree that the current version is healthier. It's now a respons to lifedraining ADCs. The old form was great against ADCs who don't have lifesteal, but most of them do in the lategame. It was also a cheap item which was mainly purchased as last or second last item, which is also pretty contradicting because you're looking more at the total stats at this point than the gold efficiency.
Balance-wise, I feel like it's a bit underpowered. Also, the addition of Cold Steel passive really hurts Rammus who would rather give their opponents an AS boost. But maybe Rammus just needs some fixing, he was heavily balanced around his item build which lead to having only one viable build, really. Now I suppose he can get the mini thornmail 
and then build other stuff.
Bramble vest is strong in lane in certain matchups, but thornmail is a little inefficient to buy in full.
Just like the last whisper GW item, it's not really best used to 1v1 anyways. It will be better in teamfights, i.e. enemy ADC doesn't get to heal up to 100 off you/if they attack you it makes them much more vulnerable to your carries killing them.
