Hi, I'm an avid Darius player that played him all the way to Diamond 1 across multiple seasons on NA (Pre and Post rework) and I'd like to share my thoughts on the Darius buffs and explain why they will not fix his problems while causing other problems in the process. On the PBE, currently, Darius is getting two very minor buffs to his kit. The changes are the following:
Crippling Strike (W) cooldown lowered from 9/8/7/6/5 to 7/6.5/6/5.5/5
Apprehend (E) armor pen increased from 5/10/15/20/25% to 10/15/20/25/30%
Let's start with the W buff. This buff essentially makes his W lvl 3 at lvl 1, and that is it. It doesn't become any stronger with levels and is now terrible to level up and feels really unrewarding to level past lvl 1. The biggest problem with this change is that his ability to level 1 cheese with W will be significantly increased, especially against melee champions, which he always has been good against excepting a few exceptions (Fiora, Yorick and Riven). This change makes him a lot more oppressive against melee champion who already have a hard time fighting him and doesn't help him scale better into the late game.
For the E buff, this change isn't bad and is quite welcome when fighting tanks who rush ninja tabi bramble and another armor item against you since you'll have an easier time pushing through their armor with the E passive and Black Cleaver. While it's a welcomed buff, it will not have much of an impact on his viability and play-ability in higher ranking brackets.
The biggest problem with these two buffs is that they will significantly increase his performance in the lower ranking brackets due to giving raw power in the early / mid game. He already does a pretty good job in Platinum and under at punishing top laners who don't know how to play him properly. However, this does nothing to help him fight more competent players and fighting ranged top laners, which are a big reason why he is unplayable right now in higher elo in my opinion.
How to address his incapibility to fight ranged champions while also not making more oppressive against melee? My first suggestion is to make his W be worth leveling again. His W should have its total AD ratio scale with points you put in it. Right now, it's 140% at every level and the only thing you get now is a mediocre 0.5 CDR per level (1 second on live). It doesn't have to be a massive increase, just a 140-160% total AD with levels would be enough to give him better damage in the later stages in the game with an higher AD ratio to scale his cleaver, his passive and his steraks. This would allow him to have bigger killing potential in a duel against a tank and punish people who allow him to get to 5 stacks to proc his passive. It could keep the live cooldown of 9-5 seconds and scratch the current buff to avoid giving him too much raw power all in one go.
My second suggestion is to make his E have more range. Before his rework, his pull had the same range, but when you casted the pull, it would pull you weather you were in range or not after the 0.25 delay, which could lead to him pulling someone who flashed away or dashed away. Obviously, while funny, this is not a good thing for the game. A similar case was Cho gath's W, which would damage and silence you in the same way that Darius E would pull you. That ability got changed on patch 6.20 in the following way:
Cooldown reduced to 13 / 12 / 11 / 10 / 9 seconds from 13.
Range increased to 650 from 585.
Silence duration reduced to 1.5 / 1.625 / 1.75 / 1.875 / 2 seconds from 1.5 / 1.75 / 2 / 2.25 / 2.5.
The biggest eye catching change to me is the 65 range increase to the cone of the W. That allowed him to still hit some champions who are at the edge while also giving you the opportunity to dodge it with good reactions. This is exactly the change Darius needs to his E. By increasing his E range from 535 to 600, this would give him that little extra bit of range to have a way easier time pulling ranged champions. The cooldown on his E is very massive and the ability has the same counterplay cho gath W does, so it's not like this would be gamebreaking and this would make him a lot more playable into Jayce and Gnar since they'd have to position better and poke with auto attacks when Darius is busy doing something else rather than freely hitting him with no fear of consequences. This would also help fix a major problem Darius has in the late game. Many of the popular and strongest ADC atm are Kog maw, Twitch and Tristana. Those three ADCs have a massive range advantage on Darius and can outrange his pull with their auto attack while doing ridiculous damage. This give very little room for Darius to actually interact with them in a teamfight. Having that little extra bit of range would give a far better chance at getting a game winning pull if he positions himself properly and help him punish miss-positions a lot easier. Again, if this range buff would to be added, I wouldn't mind losing the 5% armor pen on his E to avoid giving him too much raw power in one patch.
The current PBE changes will make him more oppressive against melee champions without helping him have a chance against ranged champions. Making his W gain 5% total ad ratio per level would help him scale into late game and give him better kill pressure on tanks. His E should gain slightly more range to have a chance at fighting long range ADCs and have an easier time fighting ranged top laners in lane.