I think the biggest distinction is that there would have to be SO MUCH investiture in the steel to change it's Axi into pure investiture, AKA Edglium.
I think at a point yes, with enough investiture, but the rate that investiture leaves nightblood is quite high, and we don;t even know if nightblood can hold that much. Someone incredibly invested, like maybe Susebron, could pour investiture into it quickly enough that the Axi begin to eject the steel and reform to be edglium or some steel-edglium-nighblood alloy, but I think at this point, nightblood is not considered a god metal, but a peice of metal with a ton of investiture dumped on it.
Also, to make a sort of comparison : When holding stormlight, you yourself are not becoming more invested. You are holding the investiture. We have no confirmation that putting a breath in a object makes that thing more invested, or rather gives it the breath to hold. some breaths in nightblood would invest it's spirit and make it sapient and allow it to talk, but others it could just be holding on to as extra food for later.