So we agree.........
I'm not so sure that we do.
For example, your earlier post says they can twist their tails to be vertical. It appears you're arguing that birds use their tail as a vertical stabilizer?
I've never seen my birds come even remotely close to doing that, even in extreme maneuvering. I've never seen video or still photos of that either. And, I'd argue that they don't
need to use their tail that way, anyway.
The yaw stabilization in birds is accomplished without the tail, or at least without the tail
dictating yaw stability. As evidence of that statement, I've seen birds with tails "removed" that were still completely able to fly and maneuver. In birds, the tail is one of many factors that
aid in stability. Whereas in aircraft, the tail does much more than
aid stability; it
allows stability.
As an analogy, I'd look at a human and say that he/she uses his/her arms to
aid in balance. The arms can even be an important factor in balance, at times. But, in removing the person's arms, do you remove their ability to balance? Nope... Much the same for removing the birds tail.
But, it's not the same when it comes to removing an airplanes tail (or even just a part of it). The tail of a bird isn't (and doesn't need to be) used like an airplanes tail. So comparing bird flight to airplane flight is already shown to have some serious flaws. I think if we looked at propulsion as well, we'd go right over the edge...