It's actually annoying , because 
is supposed to be a core item on juggernauts like Darius, but then you realise that it only increases base ad, so it does not scale your passive damage, or your dunk damage whatsoever.
Garen for example, only has total ad scalings, so he can get full benefits from without any drawbacks.
I would rather have Darius keep falling off late game, thank you for very much.
So,how come his R doesn't scale of HP? He lirerally jumps on you and cleaves you with brute force and his body weight.
Nope, nope, nope. If his passive and R could scale off total AD rather than bonus, you would have TANK Darius builds working super well, which would be a complete nightmare.
The real problem is that Sterak Gage is actually a bad item overall, because they can't balance what their concept of the item has become (major health + shield item, with the base AD increase which is practically an added bonus) without making it foolishly OP (like when ADCs noticed how good was actually the shield and started to take It).
As a lifeline/shield item it is vastly inferior than Maw (which has honestly always been stealth good and has been discovered late only because standard MR options were way too good) which give a major source of defense against what is one of the most common source of burst, aka mage burst with both MR + shield. As comparison, Sterak which share the lifeline passive, doesn't give a similar kind of double defense vs AD source of burst aka crits.
As item that increase base AD damage, Sterak is obviously behind the items of the Sheen line (Trinity or Iceborn Gauntlet) and even though Sterak stack nicely with them, you can't usually find a spot in a full build for It as if you would be going for Sterak, you'd usually go for a more damage or more utility item overall on the supposed Sterak item slot (because you have yet occupied shoes-Trinity/Iceborn-MR item-armor item at least, and you'd probably get more use out of specific items against enemy teams for the last slots)
In my opinion, they should either make Sterak the true AD anti-burst item as Maw counterpart (reducing/absorb specifically crit damage) or they should find a way ti strengthen their base AD damage item niche (swap part of shield and/or tenacity out), reducing the power budget on the item in the areas that become the minor focus
if you want that to happen. they should reduce his base values hard in order to be properly balanced in terms of health. it also makes his early game relatively shitty because of it. So, it also makes his late game worse because of how he is lacking a gap closer to catch out any ADC trying to kite him.
It can be fun to make a full ad Darius better with that change.
overall, its kinda a bad change in terms of his power.
He is a lane bully that is amazing in the early because of it.
it has nothing to do with what the other guys mentioned. as far as i understand, his ult and his q scale with bonus ad because of his passive. they want to create more pronounced windows of power.
when he gets 5 bleed stacks on an opponent, noxian might activates and darius gains 30 to 230 bonus ad dependent on his level.
theyre giving his ult a higher bonus ad scaling to make the ad bonus he gains off 5 bleed stacks more impactful.
i understand where youre coming from, but it would end as a tradeoff. if theyd give it total ad scaling, they would make it lower than the current bonus ad scaling. something like 0.5 total ad vs. 0.75 bonus ad.
this means that steraks is factored into his ult scaling, but his passive would contribute less to his ult. effectively giving it a higher base damage and lower damage at 5 stacks.
riot wants to really emphasize on the boost in power he gains at 5 bleed stacks when his passive activates, so changing the scaling to total ad would be counterproductive.
steraks gage is still a good item on darius, since he has one of the highest base ad values in the game. especially when you pair it with triforce.
It is a balanceing factor, so he couldn't build full tank, but has to build some ad as well. He gets a lot of bonus damage from his passive, but not just the noxian might, his bleed stack are bonus damage to ewen if they are damage over time. You can find the bonus ad scalings on a lot of divers as well so they can't build full tank and be effective.
