Smackdaddy,
I think I get where you are coming from, but I reckon you might be over thinking it a little.
Take the JSD page that deals with the loss of the Winston Churchill. The water moving down the face of a breaking wave can be travelling at 50kn+ (it needs to if it is to accelerate the boat to those sorts of speeds). This is inline with my own experience. It would be easy to assume that a boat restrained by a series drogue is at some point going to be sailing backwards through the water at what could only be described as a very high speed - much higher than that experienced with a sea
anchor. But, what we have is two distinct layers of water: The fast moving surface water (often full of air but still of great energy) and the relatively static water underneath. There is probably a fairly distinct boundary between the two. Unless the boat has been picked up by the fast moving water, the rudder is going remain in the lower layer. It is the series drogue or sea
anchor that ensures that the boat stays (mostly) planted in solid water.
FWIW, I use both, but most of what I read against sea anchors is just a load of bollocks...
Cheers
Peter