The Combat Crosses in LoS don't have anything to do with Alchemy.
Considering it was also made by Rinaldo, the LoS incarnation, can you be sure of that?
Also, you take a look at the way that long ass chain fits inside the hilt and you tell me that's not some magic bullshit.
And there's nothing to suggest that they had any supernatural properties; they were simply a series of particularly effective and well-crafted weapons.
Supernatural? well, Holy.
Yes. When the chain was made it was forged using holy water, and then blessed. So it's especially effective against dark creatures. (the original Combat Cross, mind you- we know nothing about Trevor's version)
In LoS, Gabriel's weapon was named "Vampire Killer" only because of its bloody reputation -- not because of any inherent power against darker creatures.
Actually, it's called Vampire Killer because of the stake attachment
So, in theory, Gabriel's CC and Richter's VK should be two very different weapons.
Classic Canon Vampire Killer would definitely be stronger, since it was specifically made to kill vampires, through the sacrifice of Sara's soul.
While the Combat Cross is simply a Holy attribute weapon with a Vampire killing stake on the end.
that said, there must be something special about that Stake, given that Alucard went back to fetch it. You'd think that any stake would do, but the specific "Vampire Killer" Combat Cross stake is what was needed. I suppose it might also have been forged with Holy water and Rinaldo magic.