Disclaimer: Longish post
I think there is some merit to this statement, but the offensive side of the Cunning Tree itself is mostly for Assassin archetypes and burst champions who thrive with Thunderlords and Precision. A lot of champions CAN fit this archetype with their all in potential; if you use all your abilities and auto attack the enemy to try to kill them, there is likely to be a lot of burst involved in this all-in. Precision certainly helps with this, but I think Thunderlord's Decree is the main problem.
I think a problem with Thunderlord's right now is that the 3 hits that proc the effect do not have to be within a short time frame. I also think that DFT is still in a pretty bad spot for AP mages right now who cannot output continuous DPS in the form of DOT or a continuum of spells (
). This is why even poke mages, who I think were meant to want to opt for Deathfire Touch, are using Thunderlord's Decree instead because the base damage on it is high enough to warrant them getting it over DFT if they cannot continuously hit their opponents with spells.
I think that there needs to be more work on Thunderlords as it sits right now, starting with giving Thunderlord's decree a shorter time window to keep the procs up. Look at Stormraider's for example, where the only way to activate the effect is to deal 30% of an enemy champion's health within 2 seconds (not hard if you're Annie). This indicates to the player that they should use everything they have to try and burst down a champion. Thunderlord's decree seems to have a 5 second window before your stacks reset on a champion. That means you can use up to 15 seconds to hit your enemy 3 times and proc the passive. This makes it INCREDIBLY abusable during the laning phase (especially if you have a range advantage) as you can tap your opponent with a ranged ability or AA, avoid harass that your enemy throws back at you and continue last hitting and just remember to keep poking them until the mastery procs and you chunk your opponent.
A more balanced version of this mastery aimed towards burst champions and assassins would be to have it so the 3 attacks must occur within 3 seconds of each other. So after the first attack you would have 3 seconds to get 2 more attacks off to proc the effect. This would eliminate the scenario where Ziggs is throwing a Q at you or auto harassing you every few seconds and still getting the benefit of the mastery.
I think another thing to consider doing with Thunderlord's is reducing its base damage just a tad. Just something to consider as it seems to just outdamage Deathfire Touch in most situations for mages (until substantial AP is built). I think yet another thing that could be done is reducing its effectiveness on ranged champions, sort of how they reduced Fervor's effectiveness on ranged champions. They could just hit the base damage here. For example: "the target takes 10 - 180 (based on level) [50% effective on ranged champions]". Honestly, this sounds a little confusing but someone at Riot could probably word it better, but I feel like ranged ADC's probably shouldn't get away with dominating the laning phase because they have a range advantage and should be looking to scale with Fervor or Warlord's which scale with Attack Speed and Crit.
Anyway, those are my thoughts on the matter right now. I think Thunderlord's should be applicable to a wide variety of champions, but its current effectiveness is much too high right now. I do think that Precision is a partial reason to invest in the Cunning tree, but it is still Thunderlord's that is bringing people to the party. I don't think that Riot will be satisfied if the changes to the Keystones (currently on the PBE) do not steer people away from Thunderlord's as much as they would like and I honestly feel like 6.1 will still be Thunderlord dominated as it is highly abusable no matter what lane you play in and is simply the best mastery for the laning phase.
Tell me your thoughts on the matter. I might post this as a new discussion entirely on why Thunderlord's is so dominant and what can be done. Now that I think about it, there is probably a Youtuber who has put up a video discussing this better than I can, but I'd still like to hear from other people. Peace.