Stormraider's Surge is the assassin mastery, for people with enormous burst like Zed and Akali. Warlord's Bloodlust is for fighters like Irelia, Olaf and even Riven who like surviving on the brink of death and outplaying their opponents 1v3. Fervor of Battle is for ADC's who auto-attack quickly and can make maximum use of the stacks and on-hit damage. Deathfire Touch is versatile, but primarily built on DPS casters like Cassiopeia and poke casters like Varus and Xerath.

Thunderlord's Decree is the mastery every champion takes instead of all those other ones, because it's strong in early laning.

As an ADC main, it really makes me mad that the meta is so early-game focused. The meta leaves me with few options, because no matter how much I want to play Kog'Maw I'm prevented from doing so because games don't run long enough for me to even start to be strong. I was overjoyed to see the recent nerf to EXP rewards from early kills: that and several other changes were geared towards reigning in the ridiculous, inevitable snowball that would take place after First Blood in the bot lane. Now with 6.15 where bot towers have no armor and give extra gold, 5v2s are inevitable (unless, of course, the other team comes to help and make it a 5v5). It's incredible that they would so utterly reverse the change they'd made to emphasize stronger late-games only a few patches before.

Possibly the best indicator of this early-focused meta is Thunderlord's Decree, which (FACT) is far inferior to every other mastery choice past 15 minutes or so. A mastery like that shouldn't be built on people who use other masteries better, unless the first 15 minutes of a game decides its outcome. Surprise surprise, after heavy, heavy nerfs since the beginning of this season, it's still by far the most-taken mastery. The reason isn't because it's the strongest option, but because it's unbalanced for the game.

Imagine if, several patches from now, late-game became all the rage and early-game champions started to disappear. Thunderlord's would also disappear because its primary benefit would not be during the portion of the game in which players had any impact on the outcome of the game. Unlike Fervor of Battle and DFT, it wouldn't continue to be picked on champions with good synergy, because its power would still be less post 15 minutes. This mastery is, in short, not taken on a per-champion basis, but on a per-meta basis, and that's really dumb to me and an example of bad design.

Continuing the Deathfire Touch compasion, another reason people love TLD is because the damage is dealt instantly, in a flash of lightning. DFT deals damage over time and is mostly invisible, so people don't take it when they should, because they don't realize that it has any effect. This is the same flawed logic as taking 1% crit rune: 1 AD most certainly is a more effective rune and can win your lane without you ever realizing it: 1 CS here you would have otherwise missed, 10 bonus damage from 10 auto-attacks winning you a trade, etc. But a crit looks big and impressive, and when people win with 1% crit they attribute it to the rune, not to the 1 million other, more important factors.

The final reason I hate Thunderlord's Decree is because the entire Cunning mastery tree is so generic and universally useful to anyone who invests points into it. There's no downside to taking points in that tree, and the whole idea of choosing between 3 trees falls apart when you can take the same 18 points on every champion and do just as well, if not better. The keystone has the exact same problem, and so it gets under my skin even more for being at the top of that tree. But that's it for this rant, I don't have any sort of graceful conclusion to wrap this up. Bye.