Yeah there's a clear, defined difference between the Caledor's Bane Lance and the First Draich, namely that one of them was created by the Forge-Priests of Vaul, in fiery devotion for a truly excellent weapon. As much as some Asur might not like to think about it, there are Gods that lend a hand to just, you know, Elves in general, not just the Druchii or Asur. There are Asur worshippers of Anath Raema, for instance, as well. And there are definitely some Druchii mothers who murmur prayers to Isha that they give birth to healthy, strong children. Because, you know, otherwise, shame and hatred and loss of position on society, so please no dead stillborn or weak children please, etc. Or perhaps because they genuinely just want a child that lives well and long, who can say for certain for every single Druchii mother.
But yeah, the difference is, Forge-Priests of Vaul making a very good lance. Didn't have to be specifically to kill dragons, either. It was just making a super good lance. That, you know, could also pierce the chest of a Greater Daemon, or a Chaos Dragon, or a Giant, etc. etc. Though, yes, it was forged by Druchii, for Druchii, so it is likely intended to at some point be used against the Asur, either riding Dragons or Gryphons or Great Eagles or whatever. The point is, though, is that Caledor's Bane (the lance) ONLY got its name and dread reputation as Caledor's Bane (the lance) because it was wielded by Maranith, who would be the one using it to kill so many Caledorian Dragon Princes and Princesses and their Dragons, and got his title as Caledor's Bane (the person) and would rather amusingly have his weapon named after him. It would be like if Frederick ran around with an unnamed but powerful runic blade that became called the Steel Bull, or one of his other titles. Same sort of thing.
The First Draich, on the other hand, is utterly soaked in blood and pain and suffering. It was not even made specifically for ritual purposes, and is noted to explicitly have been a guard's weapon. Some rando Druchii who was standing guard as the first great sacrifices were made in Har Ganeth long ages ago, when the cities of Naggaroth were first forged. And Tullaris took his sword and started killing, showering in the blood spray, and so the Har Ganeth Executioners were born. Given its stats, its possible to have been made by the Forge-Smiths of Vaul, but like, for a highly placed guard. In that time since, however, it has long since discarded any touch of Vaul if there were any, for it has solely been used for sacrifice and empowerment and showing devotion to Khaine for all that time. It thirsts for blood, an echo of Khaine's own thirst for murder. I would argue, in fact, that it wasn't strictly a magical creation of the Forge-Priests, just a good sword taken straight outta the hands of a random if highly placed Druchii Guard and then so soaked in blood and murder by the Hand of Khaine for so long and so thoroughly that it has gained its properties through the blessings of Khaine upon it.
The Lance, by contrast, just plain old doesn't have all that.
Also, yeah, as noted in the Armybook, Malekith claims to be Khaine's mortal avatar purely for the accompanying political advantage, and also notes that unlike the Witch King Tullaris is the true herald. His dreams and every waking hour are filled by violent whispers, and he doesn't challenge Malekith over the matter of who Khaine likes most "simply because the Lord of Murder has not yet commanded him to do so."
Also, not like it matters because we all know that TT numbers aren't the most perfectly reliable things for DoDA stuff, but also 'ooh ahh numbers'
Tullaris: M 5 / WS 6 / BS 6 / S 4 / T 3 / W 2 / I 7 / A 3 / LD 9
Malekith: M 5 / WS 8 / BS 7 / S 5 / T 4 / W 3 / I 8 / A 4 / LD 10
Kurt Helborg: M 4 / WS 7 / BS 6 / S 4 / T 4 / W 3 / I 6 / A 4 / LD 9
Korhil: M 5 / WS 6 / BS 6 / S 4 / T 3 / W 2 / I 7 / A 3 / LD 9
Tyrion: M 5 / WS 9 / BS 7 / S 4 / T 3 / W 4 / I 10 / A 4 / LD 10
Araloth: M 5 / WS 8 / BS 7 / S 4 / T 3 / W 3 / I 8 / A 5 / LD 10
Orion: M 9 / WS 8 / BS 8 / S 6 / T 5 / W 5 / I 9 / A 5 / LD 10
So, you know. Numbers from TT ain't precisely the be all end all, yeah?