The fact that the world hasn't been completely overrun by vampires indicates that vampires don't have disease level reproduction otherwise they would win one vamp could easily create dozen more who could create dozens more etc an never wave of super powered death, KoC can't fight dozens of black court vampires they are only humans and wizards would be over run, cities could be overrun in days where talking end of days territory. So given they don't have disease level growth how fast to people think they can reproduce? (White Wolf Vamps don't have that level of reproduction either siring kindred is a big effort on the part of vampires).
Punctuation.
Sorry. In all seriousness. I think you already decided the answer to your question. They can infact do it. No one can stop them. They win. It is the end of days. This is goingto sound rude and to some extent it is. I have to ask though. If you seem to have the answer already decided in your mind...why ask our opinions? I can tell you I agree and let you hear what you seem to want...but I'd be lying.
Also, Knights can totally fight dozens of vamps. That is what they are for, saving the world from evil. They have Archangels backing them up.
Wizards proved they can kill hordes of vampires in a novel called Changes.
I even just explained how to do it as a Knight. Been there done that. (BCVs and RCVs) Random people made into vampires do not turn into martial arts masters like in Buffyverse. Their skills will not match what combat veterans can do. A measly +1, +2, or, +3 combat skill will not match up to +5 or +6. I've seen teamwork in action before also in this game. It doesn't work quite as well as it sounds.
I answered your question fine.
The setting (assuming you ascribe to that and are asking about our opinions with that setting and canon in mind...) pretty much couldn't exist if BCV could make armies of powerful vampires.
Keeping with canon and setting established by Jim Butcher and the setting used by Evil Hat to create the DFRPG - I give you this explanation:
If vampires could do it; they would have by now. The fact that they haven't means they can't. I give vampires enough credit to think of that on their own. I could see them making as many people as they could bite in an evening (assuming that is how they make more). I just don't think it matters or that they are of any sufficient quality.
Again I draw attention to "It's My Birthday Too". Several vamps were made in that short time frame. It can't take long, but they sure didn't seem very powerful.
In your own setting they can be as powerful as you want. They can reproduce as fast as you want. They can be Bruce Lee as soon as they get made.
If you want me to come up with a sane arbitrary number? I'll just go with Sanctaphrax's idea. Or let them make thousands and rule the world. Your game, your setting, your rules.
As an aside:
V:tM has rules for mass Embracing via the Sabbat Ritae. The vampires come out by the droves. They suck compared to most vampires. Seriously, if you make an army of vampires you can't be picky and usually get busses of cheerleaders heading to football games. (Or maybe that was just my favorite for shovelheads)...
