Questions regarding the design choices (and intent) of Thunderlord's Decree

From the 6.1 patch notes:

While Thunderlord's Decree is the go-to mastery when you're looking to dominate your lane [...] It's something you can easily play around, has a good amount of impact, and synergises well with certain champion kits. [...] better ecosystem for Keystones where you're free to adapt your builds, rather than (...) abuse the best mastery. Injecting some strength back into Ferocity's Keystones (...) should help balance things out, no matter how you seek to deal your damage.

It appears (and I'd be happy to stand corrected if I'm wrong) that Riot intends DFT to be more of a poking/harassing tool, better at sieging and the objective standstills later on, while TDL is the more interactive of the two, favoring short burst and trades (and leaving you exposed to retaliation since you need to stay in range for several hits to trigger it).

However, what happens a lot instead with TDL is that either both players have it, and as long as they hit thrice then it doesn't make a difference (apart from people dying quicker), or one player can apply leverage (only him has TDL, or enough of a range advantage that he can apply the first hit safely). In the second case, getting hit by a single spell or auto forces you to retaliate (with poke, or by committing if you don't have the range, which is a big thing) or play defensively until the counter resets, because your opponent is now so close to triggering TDL and it's going to make a bigger health differential than a normal trade.

An apt comparison would be Kennen, since as long as he marks you once his Q becomes a lot more dangerous, and the reliability of both W's passive and active tends to make people zone themselves out of his effective range until the marks clear up. But that's a hallmark of his laning gameplay. TDL warps your behaviour by making any stray hit into a bigger threat (which is the opposite of poke), especially in ranged vs melee match-ups where a single autoattack goes from harass/a punished last hit into potential burst, or in duo lanes when squishies are involved (since 2 TDLs = double the additional damage).

Having to take masteries into account isn't a bad thing, however its dynamic tends to supersede kits, especially for champions who aren't about burst and wouldn't feel dangerous with their main tool on cooldown (Ziggs, Lucian/Corki who just used Q+passive to last hit, etc.). It is something you can play around, does Riot deem it desirable that it requires so much playing around as soon as it comes into play however?

The second big thing about TDL is that it rarely requires commitment: if you've got some long range tool, once you get your first stack you don't really need to all-in to trigger it. Which actually works very well for poke/safe champions! I assume that the "3-hits rule" is invoked here to give the opponent time to react, to justify TDL's damage by making it non-trivial to apply for the user, and to generally make the whole thing more interactive. However, because 3 spells/auto is so easy to apply, it seems to devolve into an "oh sh-" moment for the victim, trying to avoid incoming hits, rather than an effort for the user or a dance between them.

What are the reasons behind 3, specifically? Is it some kind of "norm" now, wrt the other 3-hits passives? I'd like to go back to the quote at the top of the thread: the patch note mentions TDL as "the go-to mastery to dominate lane", which seems to imply that it has more impact there (and as a result less impact than others later in the game). Laning features more trading of auto attacks without committing, especially for ranged champions, be them magic casters or marksmen, something that tends to disappear as the game progresses (the same way Brand may harass with E, but will stop in favour of the less reliable Q/W once walking within 600 range of the grouped enemy is asking to get jumped on and killed). If tailoring the mastery for laning, would raising the number of hits (for example to 5) to force players to mix autoattacks and spells, be a reasonable approach?

It forces attackers to commit and actually burst/trade, rather than sit back and apply pressure/trigger TDL from safety, and synergises with Precision's hybrid nature, especially for mages. The damage could be adjusted accordingly, both because it's now harder to attain early, and also riskier later on (especially for non-Azir/Kayle/etc. AP-based champions, whose casting range typically exceed the aa one and whose autos don't deal much damage by themselves at that point). (Potential) gains could be todifferentiate its pattern from DFT better, give more time to react while being less punishing for immobile, or melee vs ranged match-ups, and getting more impact out of it as a reward.

I guess the main question is "how did you intend to make DFT and TDL's use cases branch out?", from a situation where unless you're a Liandry's user, TDL's ease of use/triggering usually trumps its brethen.