I wanted to do a thread on that too but it takes a heckofalotof research and math, mostly math, to make full comprehensive comparisons between the old and new mastery trees. And that's no good for a lazy person like moi.
Thing is though, the only contenders for keystones that overloaded the game with damage are Thunderlord's and Fervor (and maybe DFT). And while I had to find out that lv 18 fervor gives AAs more damage than the masteries in previous seasons, there's also the fact that those masteries gave more AD (since ADCs have to take 2%LS/SV these days) and AS.
Thunderlord's ... yeah it'll secure you some kills but you gotta admit it's a really fair mastery. 3 damage sources need to connect, which aside from weird interactions like Heimer rockets, is something you can prepare and defend yourself against. And a min 15s CD for an ability with terrible scaling and average base damage is pretty fair too.
Haven't given DFT much thought. It's good for trades when used by champions with singletarget spells and more of a scaling ability that combine with a lot of AD or with Rylai's. With all the sustain in the game, I'd say there're enough counters to it. Idk.
Thanks for the upvote tho^