I might be "beating a dead horse: about the of "Demanican Justice vs Noxian Guillotine"
But, people need to understand the exact usage, and not how "one can outperform the other because Magic DMG vs True DMG, Refreshing CD"
Putting damage side, what does DJ do well that NG can't? For one, I see that DJ will out scale NG in damage based on what the target is stacking/lacking. Against Tanks, DJ will almost always maim, to permanently, injure the tank so it puts him/her out of use. But one will say then they wasted everything on the tank, I only see it as a waste if they didnt allow Garen to expend his ulti to cripple the tank. (Note: 525 + (40% maximum hp missing))
As offtank Garen he has the ability to "CHARGE" in wif Q and W, if he so wished to do so then the enemy team must stop him before he can reach their prized carries in the backlines. Garen's utli has proven its deadly presense through time and experience by being the "FUCKING SWORD FROM THE SKY" so it has an innate ability to give off a big scare forcing the ADC or APC out of the group. (Note: The natural highest amount of MR ADC has is below 55, anymore is due to items or runes; and who really stacks major MR on ADC)
Lastly, as a skill that CANNOT REFRESH it puts it on a much higher value than NG, if wasted then Garen's chance of INSTANTLY turning a fight into a 5v4 is gone. Plus becuz it has a huge value (again due to the high CD and one time use) it will force more thought into being used solely to "simply ks my team."
For NG, it main use is to kill the target, secondly it to kill the target and refresh the Ulti. True DMG is no joke, nothing (but HP) can stop it from completely killing you. It is designed to kill the already weakened champions that are either caught out, or taken its toll in the battle. But ask, how can Darius get in? I'm sure no one is stupid enough to stick close to Darius to get pulled in. Darius himself risks his own life charging into the battle as he does not have anything in his kit to defend him self or allow himself to survive if he solely built to do the maximum dmg as possible.
NG does not give an INSTANT sense of fear. It only scales (340 (+ 75% Bonus AD) - 680 (+ 150% Bonus AD) based on the number of hemorrhage stack on the target. When, does Darius ever have fully applied 5 stacks on a WELL PROTECTED target? I will agree that a maximum of at least 3 stacks are present but thats only a 60% increase. Now assuming that the Darius has 200 AD (113 base at lvl 18 + 87 bonus AD) that means only 75% is converted into the DMG (340 + 65.25 to 680 + 130.5 or 544 + 104.4 for 3 stacks). It only out scales DJ base dmg after 2 stacks but it doesn't even start to outscale it entirely.
Lastly, a skill that DOES refresh gives it a sense of a skill that can be simply thrown in when deemed suited for the mood. Sure, one may say i can simply allow the target to walk away becuz Hemorrhage will kill him/her, allow me to ask, "you will depend on a passive to end a failed attempt? What if a shield was applied as you walked away? An enemy managed to get healed? Worse, you now don't have an ulti to use when the enemy team counter attacks."
Now comparing that two skills to a very common debate "KS-ing", the way I see it Garen has ONE attempt vs Darius's possibility of FIVE attempts. Who will starve whose team more?
Compare Kit wise: Garen is naturally tanky, has a silence, and AOE DMG over 3 seconds, as Darius is AOE DMG based on his targets either being next to him or at the edge of his Q, He has a ATKSPD and MS slow, and %age Armor Pen pull. Of course you not going to run in as Darius, you await to single out a target for your team. As Garen you charge in to announce the target to your team.
Lets Compare DMG:
(Using a 1000/2000/3000 HP target) (And assuming if the target is above the base Magic Dmg)
Lvl 1 175 to 175 + 235 (1000 - 175) + 521.4 (2000 - 175) + 807 (3000 - 175)
Lvl 2 350 to 350 + 550 (2000 - 350) + 883.3 (3000 - 350)
Lvl 3 525 to 525 + 589.99 (2000 - 525) + 990 (3000 - 525)
Note: THIS IS THE RAW DMG, THIS IS WHY YOU DONT SUGGEST TRUE DMG FOR GAREN
(Using 100/200/300 AD and only 0 or 5 stacks)
Lvl 1 160 + 21.75 (lvl 6 is base 71 AD so its 29 Bonus) to 320 + 43.5
Lvl 2 250 + 83.625 (lvl 11 is base 88.5 so its 111.5 Bonus) to 500 + 167.25
Lvl 3 340 + 145.5 (lvl 16 is base 106 so its 194 Bonus) to 680 + 291
Note: ASSUMING THE HE ONLY GETS THIS MUCH AD AT THE LVLS I POSTED
Now assuming that the target is stacking enough MR to HALVE Garen's Magic dmg then it comes to:
(using lvl 3 Ulti)
557.495 (for 2000hp) and 757.5 (for 3000hp)
Understand these numbers and Understand their different usage before bashing on which ultimate is better DJ or NG. Small note: Garen has a choice who to ulti when he see that either target is low on HP, Darius will almost always choose to Ulti the one that has the most Stack so he is almost certain to refresh the ability.
Special Note: I would like to Thank BoroPaladin and one Anon to correcting my mistakes
BoroPaladin for Numbers Miscalulation and
"The main difference between the two, really, is their ideal target: Noxian Guilliotine wants to be hitting something with low health so that it's more likely to kill (as armor and MRes don't matter), while Demacian Justice wants to finish off the tank" -- BoroPaladin
The Anon for suggesting that Garen's Ulti can be used outside of "Tank Busting" and
" 100 Mr isn't too detrimental to DJ damage, but 140 definitely dents it to a noticeable degree, to the point I feel you are much better off slicing a squishier target with a greater damage threat to your team, than a tank who will just be highly aggrevating." -- Anon as well as
"Another minor issue with your example is, not many Darius' (As foolish as most are) would be inclined to build pure AD. That is suicide and no Noxian Guillotine is going to save him from spontaneously combusting the second he exposes himself. The major reason NG is compared to DJ is because of its spam-happy nature, while simultaneously, Darius being able to endure tank level punishment while still being a stupidly high threat to the team, simply due to the spam happy nature of his ultimate. " -- Anon