I think Kelsier with a regular shardblade would be almost as terrifying as him with Nightblood.
Nightblood is definitely much more powerful and the combination would result in a lot of murder, but since Kelsier’s a cognitive shadow and has… questionable morals I don’t think he would be able to wield Nightblood for very long.
A regular shardblade, however? It’s powerful, can’t be influenced allomantically, and can be summoned and dismissed at will so shouldn’t have an impact on pushing/pulling.
It doesn’t even have to be a Radiant blade for him to cause a lot of damage.











