-Can D operate at hypersonic speed (Alucard caught bullet with his mouth which was hypersonic).
-The same bullet was able to devastate SR-71 aka Blackbird which is actually tougher than ordinary jet fighter (can go into stratosphere so needs to be from taugher material) and he couldn't pierce Alucard's chick(only hurt his chick). So as you see Alucard is actually very durable, he only allow himself to be injured in order to downgrade opponent. And Alucard was in his standard red-Victorian coat and black suit form.
- The standard weapons for killing vampires don't work for Alucard (heart stabbing and head cutting ). D is able to be killed and needs to cover himself with ground to regain his strength.
- He has a greater strength than D by great amount I would say.
- HIs total power is far greater than what D has shown.
Those are only several reason for which I thinka Alucard takes this one (I'm to lazy right now to post other reasons, but if anyone insist I'll post them).
I'm not great expert on D i only have moderate knowledge, but judge from what I've seen (including some of the best D's manga feats) I don't see how will he go past Alucard. At best I would put D on the same level as Jan Valentine who is << Alucard.