Darius is actually getting x2 indirect buffs along with his 8.4 buff
So I've just played a few games Vs the updated Darius and I have to say with more coming RIOT have you really though this through? He is noticeably more oppressive as it is it's simply impossible to outtrade him now if he's competent.
So in 8.4 he gets an armour pen buff with his E and more dmg on his W. That's the first buff.
But the additional 5 minion damage is also getting or has got removed. This won't affect him so much because of his bleed ticks meaning he doesn't necessarily need to last hit to kill a minion whereas other champions do. This gives him a degree of options during lane phase to punish whilst also farming.
And finally we have the upcoming bruiser keystone. Which I'm not against but surely it would have been better waiting for that keystone before deciding to buff him? It will just be a buff ontop of a buff. In a nutshell with his buff and this it's an AD and armour increase buff then a keystone that amplifies it further. Im positive it'll be busted on him.