Also, Black Keys are conceptual weapons, something Alucard has shown no resistance against.
Conceptual weapons are made in mind to counteract a single soul's immortal status. You seem to forget that Alucard is a collective of the millions of souls that were slain throughout the centuries he has been alive and Black Keys are known for being the bottom of the barrel in terms of attack strength and proficiency, thus I doubt they can effect Alucard.
Regardless, Alucard is in almost all ways inferior to Arcueid
One of the few things I agree with, though I find this to be an unfair comparison since Arcueid's an abstract being who is a life-wiper at her full power.
even some of the dead apostles like Nero, and the black keys could hurt them.
Now we seem to be downplaying Alucard. Nero would be comparable to Alucard in terms of the collective status they have. In addition, Ciel's Black Keys were having no effect on Nero when she combated him as Nero's body isn't the typical variety of Dead Apostle due to being a manifestation of chaos. Dealing with Alucard via Black Keys would be no different in that regard.