@Vamathi Well, an entertaining theory, if it wasn't for the fact that the old source books and info about greater vampires have been heavily retconned. That's my main problem with our current D&D lore, it's been so heavily retonned on so many aspects that it's very hard to tell how stuff works sometimes.
For example - all vampires in BG2 seemed to be independent, so not really spawns, and on top of that at higher lvls 'greater vampires' were quite a common enemy in BG2. So we know that the way vampires work has been changed in 3e. BG1/2 = 2e. So I highly doubt Astarion is a greater vampire, like I said - if he was indeed mind controlling you, you wouldn't be able to kick him out of your camp entirely (after him trying to bite you). If he was a greater vampire, and you were dire charmed, it would be impossible to say no to him. So no, you've gone a bit off the deep end with your theory. Basically, you have an idea that he's more than he is and you are grasping at any straws to prove your theory. Look at it all logically with an open mind.
Is Astarion old? Yes.
Does it make sense for a 'greater vampire' to start off at lvl 1? No.
Does it make sense for a vampire spawn to start at lvl 1? Not really, but since he's supposed to be a much weaker version of a vampire, it's at least plausible.
Does it make sense for Astarion to start at lvl 1? Yes and no. If he spent all his 200 years of vampirism being an errand boy for Cazador and wasn't allowed a drop of human blood (could be elven etc) then sure.
Does it make sense for a vampire spawn to have access to dire charm at lvl 1? No.
Does Astarion lie about Cazador? No. Watch this:
https://www.youtube.com/watch?v=D5U7cWMyz3I (most of your theories fall apart after watching this - considering it's from his point of view - basically he can't be serving Cazador while this is his reaction).
Is Astarion absolutely terrified of Cazador? Yes, for a good reason. We don't know the extent of Cazador's abuse. And Astarion isn't really forthcoming with information, not yet anyway.
Is being charming a part of Astarion's personality or is it due to his vampirism? I think it could be both.
Now does it make sense for Astarion to be a lvl 1 700 yr old elven vampire spawn? Why not? If he wasted his time in life seeking wealth (and according to some old PR material on him, it was implied that he was quite ruthless in life anyway) and partying, mingling in high societies, then why not? And the 200 years he spent being a slave, it's not like he would be allowed any personal growth.
That's the thing, your theory is all fun, but it's way too convoluted. I'd say - the resolution to it all is most likely going to be quite simple.
