It's two sides of the same coin. Alpha Legion destroy from within, undermining the structure their enemy relies on. Night Lords are much closer to what the quote describes. Piece by piece, inch by inch, they will kill you and let you know about it. Alpha Legion are more about quietly ending someone.

Since at least one primarch for AL is still alive, their equipment would be utilized too.

Namely the Pythian Scales

"The armour was fashioned after the shadowed mythic age of Ancient Terra and could turn aside any blade, energy blast or alchemical attack with equal ease."

and the Pale Spear

"The Pale Spear was one of a number of strange and esoteric weapons associated with the PrimarchAlpharius. Rumoured to be a strange Xeno artefact, whose forging predated even the rise of the Eldar, the double-bladed spear seemingly flickered out of phase with the material universe and emitted an eerie and otherworldly howl, when wielded. It was capable of piercing and ripping apart any physical defense it encountered; while against living matter, The Pale Spear inflicted hideously bloodless gaping wounds on its targets, as the flesh where it struck dissolved into oily smoke"

as with anything with AL though... we have to be suspicious about it.

EDIT: i'm not sure about this practice, but the lexicanum has this on their info.

Alpharius wore at least four sets of Armour before the Heresy he had discarded when they showed signs to identify him[3]. To disguise Alpharius Omegon further members of the Alpha Legion would drink a substance mixed with the Primarch's blood that seems to temporarily turn them into him. The disguise is so convincing that even the Legion's own Apothecaries are fooled by it, and those who undertake the process are even given some of their Primarch's memories.

this opens the possibility of demi-primarch marines doesn't it? Not all, of course, but the force personally led by Alpharius/Omegon/Alpharius Omegon.

I know it's off topic, but I was wondering if anyone well versed in Alpha Legion Fluff could enlighten me on if their legion actually had a civil war between Alpharius and Omegon. I heard they split their legion in two, 1 staying loyal to Chaos and actively destroying the imperium (Which I think was Omegons side) and the other still trying to destroy Chaos from within. Can anyone comment on this, if it's true or just speculation?

So I don't think anyone can be an expert on AL because of the sparse material and unreliable narrator with them. But Black Library had a test of 'which are you, alpharius or omegon' which suggests one is loyal to the spirit of the emperor, and the other is focused on matrial prowess. In the bits i've read personally, they're unified enough not to step on each other's feet but every splinter group is different and independent. It's no even clear if Alpharius or Omegon even appeared in Legion (HH book). They treat the name's as a suit you wear for an occasion rather than their primarch. Example: anyone who shows up looking like Alpharius for the event will be named as such. the head of the stealth squad will in turn take Omegon as a name.

Legion paints them as loyalist renegades, potentially. Others they're full on evil chaos. Both could be correct at the same time with the splintered nature of AL.

Alpha Legion vs Night Lords is actually Alpha Legion vs Alpha Legion disguised as Night Lords

Actual Night Lords win by default

nice try, Alpha Legion hasn't been known for fighting each other haha.

Not sure if serious.

has definitely happened

playing up the unreliable narrator thing, don't worry.

either way, votes are coming in.

EDIT: was scouring the logs on wh40k wiki and the AL. they made the Space Wolves run away and get bailed out by the Dark Angles (naval fighting). along with a host of other fights. I found this in their data.

When the time for an attack came however, it would be a tactical mistake to underestimate the Alpha Legion's abilities in open warfare, abilities which had drawn grudging praise from both the Warmaster Horus and Sanguinius in action. The members' tactical coherence and fluid mastery of complex stratagems deployed by the Alpha Legion in the realms of infiltration and covert assault also made them masters of eloquent manoeuvres, feints and ambush in open battle. To fight the Alpha Legion's warriors and war machines in open battle was akin to fighting a single, vast and crushing entity with mystical limbs and striking fangs, but operating under a single malevolent will.

EDIT2: At a strategic level the Alpha Legion was clearly at pains to maintain a wide spectrum of military assets and capacities, its dedication to flexibility ensuring it was as capable in armoured warfare as it was in surgical drop strikes, artillery fire support or close-quarter Zone Mortalis operations. It was supported in maintaining these abilities by voracious demand for matèriel, particularly supplied by Forge Worlds such as Lucius, Incaladion and Phaeton -- with some of these treaties of provender brokered directly by the Warmaster Horus, no doubt in the hope of further securing the Alpha Legion's loyalty. These arrangements do not, however, account for the full scope of the Alpha Legion's extensive panoply of war, particularly their known acquisition of rare and specialised wargear notionally only manufactored by the armouries of certain Legions and never released to others, or not yet issued outside of close prototype deployments.

i'll stop, or else i'll just end up copy/pasting the entire wiki

After some serious consideration, i'm abstaining from this round. Even after playing out their strengths, weaknesses, scenarios, primarchs and prior victories over and over again, it's hard to come up with any decisive victory or even key aspects which might allow one to truly overcome the other.