I'd like to stress the differences between my real 3D (a) and your fake 3D (b).
1) Looking at 3D(a) scene, a spectator can focus his eyes on whatever point he wants, whereas the 3D(b) scene offers only one focus plan, which leads to problems and this is the whole point of my previous post and its parent post.
2) Fixed and non fixed perspective exists for both 3D(a) and 3D(b), so I don't get your argument here.
Fixed for 3D(a) is achieved by not being able to move relatively to the displayed scene (just sit there), and non fixed for 3D(b) is available with headset,walking pad, and CGI.
3) A simple test that I recommend to you: experiment real 3D(a) with only one eye and fixed perspective !
If you don't have a real 3D display in your lab, use the real world instead: Close one eye, look at the horizon through the window, don't move, then watch a dust on the glass (your eye just changes focus). You won't see the same thing, will you? Try this with your fake 3D(b): not possible.
4) Your equation 2D+depth=3D is only valid when depth isn't only a limited feeling of depth, as provided by stereoscopic pictures.
Again this limitation that I stress is the point of my previous post and its parent.
5) Startrek holograms, or today's lab real 3D displays, are not stereoscopy, even with a very pedantic sense. Why? See previous points 1,3,4.
I hope those differences will enlight you and demonstrate the vast superiority of real 3D display (that I call 3D for short) and your fake 3D (the stereoscopic effect).
Let's face it: so called 3D movies today are a marketing scam, and I wonder:
How will they call the real 3D display when it gets out of labs to be in mass products?
Even "real 3D" is already used by the stereoscopic movies... So?