Its not Thunderlord, its the ferocity tree
Credentials: (skip to get to the point) Been playing the game since winter of 09. I get bored of playing certain champs for so long, so i play them all, accumulating hundreds of games with almost every champ. Usually hybrids with wonky builds, and iv accumulated 100k takedowns on my two main accounts. This is what keeps the game fun for me, achieving double digit kills on average in all my games.
Thunderlords is a strong keystone right now, and its not just because its really good on just about everybody, to include ADCS like Lucian who benefit heavily from 45% cdr. The main reason thunderlord is the tits is because the entire cunning tree much stronger to all the other masteries in the other trees. Just about every single mastery on that tree surpasses anything you can pick up in ferocity. Ill explain
keystones themselves are a good idea, because it is nice to be able to play one champ in a variety of ways, this is whats fun about hybrid builds and ratios (poor poppy). The gripe i had with the mastery rework is when you are not speccing one point to get something amazing, you are dumping 5 points to get something mediocre at best, or downright awful in the case of the ferocity tree. EVERYTHING in the cunning tree is good to pick up, and the ferocity tree is by far the weakest of the 3. Every one of the 5 point teirs pales in comparison and you are effectively spending 15 points on jacksh** when you go ferocity keystone.
Which is better; would you rather deal 5% more dmg to champions with 40% hp or have 2% lifesteal/10ad15ap Would you rather have 7% pen, or 5-14 flat pen/5% cdr, which is pretty much better at every stage of the game.
The flat hp change to resolve trees makes it a good option for fighters looking to spec into that, however ferocity is weaker then ever. Yes deathfire probably needs to be buffed, and i would honestly remove warlords bloodlust all together and replace it with another mastery (and ill explain this reasoning if you would like.) However the fact remains, its because of the other masteries in the cunning tree that people are not spending all their points on the weaksauce balogn of ferocity.
TLDR: all the weakest masteries are in the ferocity tree, buff those and people will take those keystones more
First iv posted in a long time Good luck and have fun out there