although it looks similar and has a similar concept, i wouldn't really call it an equivalent to soul greatsword the way you'd call great soul dregs equivalent to CSS, or great deep soul equivalent to great heavy soul arrow, or affinity to homing crystal soulmass. dark edge does way more damage per spellbuff than either soul greatsword or old moonlight. so i kinda view it as its own thing. i think they tried to balance its poor animation with higher damage, the same way they treat ultra weapons in general. but even with max casting speed, the animation is even slower than a greathammer R1, and it has substantially less hyper armor. although it does way more damage than anything but ledo's buffed 2hR1, in dark souls 3 rolls are cheap and have insane iframes, so damage matters a lot less than the ability to simply hit people. of course just like ultra weapons, it can perform really well in invasions where players are distracted by other*****, and where burst damage is way better than steady damage since phantoms cover each other and heal if you don't kill them fast enough. so it has its place for sure but they kinda missed the mark on balancing it compared to heavy weapons. if it had a lot of hyper armor i think it'd be a lot more viable. as it is, if this is your intended playstyle, you'll do so much better using offensive miracles like sunlight spear, lightning stake, lightning storm, etc. with unfaltering prayer. it has basically the same application, close range offensive spells, but way more hyper armor and equivalent damage, or better in the case of sunlight spear. even lifehunt scythe is better honestly, as it does almost as much damage but with unfaltering prayer access and a secondary healing effect which matters a lot since the real application of all these melee-range spells, in practice, is trading with opponents who erroneously think they can interrupt you if they just keep spamming R1. in those cases, you want the most damage and the most hyper armor possible, so sunlight spear is the absolute best in those cases. after all if they can interrupt you then you pose no threat anyway. and if they can't interrupt you, it still has to catch the player by surprise. it usually only works the first time, so if the spell leaves them with 5% HP then you may as well not have cast it at all. if you spend a lot of time trying spell builds in pvp you'll probably come to the same conclusion, that there are really only a few viable dedicated spell strategies: 1) ranged casting which is best with regular sorceries or CBV; 2) black flame + black serpent + CBV builds which either use the demon's scar true combo, or parting flame + lothric war banner to maximize damage; and 3) huge burst damage surprise trading builds, which are totally dominated by a couple offensive miracles due to unfaltering prayer having a completely different hyper armor system that equates to WAY more hyper armor than any pyromancy or sorcery. and from soft just adds insult to injury - not only does sunlight spear get way more hyper armor, it does significantly more damage for a 125 build, it has a much less wonky hitbox, AND it casts faster. and on top of all that it's not even a melee spell, like it works best at melee range in practice but you can snipe people running away with it too, and you can't do that with dark edge. in fact you can hardly even do that with any dark sorceries since the projectiles move slower than a person can run. they do accelerate, but by the time they reach running speed the player has run so far ahead that the projectile will disappear before it catches up with them. so even though i think dark edge was not intended to be equivalent to any sorcery, miracle, or pyromancy, its balance was just botched relative to other attacks in general. which is also true for soul greatsword, old moonlight, lifehunt scythe, flame fan, etc. they just didn't realize how important hyper armor would be. they made catalyst weapon arts diverse and tried to make them equal but they underestimated the power of unfaltering prayer, and never fixed it. i don't think they should have nerfed unfaltering prayer of course, it's the only thing that makes miracle builds viable in invasions, and it's not even good enough to make them truly viable in 1v1 matches. like they needed to give every other catalyst a decent weapon art to match, or increase the innate hyper armor of all the slow casting, melee-range spells in the game. instead, staffs get a weapon art that slightly buffs damage; chimes get a weapon art that sees no use except for one specific chime with a marginally more practical heal; and pyromancy flames get a weapon art that is so pointless that many players are not even aware of its existence. and talismans get a weapon art that lets them poise ANY spell through 1 or even 2 greathammer 2hR1s. so in that sense every melee range spell that is not a miracle sucks fat balls. they all see very little use except by novice players or people intentionally challenging themselves with fun spells like lifehunt scythe and dorhys' gnawing and so on. so yeah it's not so much that dark edge is worse than soul greatsword, it's that all of the melee spells are way, way, way worse than all the offensive miracles. even in PVE they are worse than miracles just by virtue of the fact that many bosses attack faster than the spells' animations. but i'd say it doesn't matter much since nobody uses melee range spells in PVE, as the ranged spells do more damage and don't put you in harm's way. black flame is a different situation entirely, since its casting animation is as fast as a straight sword. it's probably the best pvp spell, pound for pound. but if we're talking specifically invasions, from the POV of the invader, sunlight spear might be the best spell because it can one-shot phantoms. that just has so much value for an invader that it can outweigh all the advantages of black flame. but yeah it depends who you're playing against, since experienced players will know what you're doing and roll away, not keep spamming R1.