Fine - show me the images with the same spacial resolution as those shot the way I said. I'll help you out - you can't. I've already done this experiment, and the teleconverters do indeed drastically improve the overall system spacial resolution despite very slightly decreasing the optical resolution. This is exactly why we need more pixels, and a whole lot more - so we aren't undersampling the optics in the first place.
Have you ever wondered why the best amateur planetary imagers operate pixels that are about the size of those on the 40D through optics set at f/30? According to you, they're way, way beyond the capability of those optics, yet they increased focal length to that level in an effort to preserve maximum detail. Why would they use expensive barlows (Televue Powermates) if those small pixels were extracting all the detail from their bare f/11 optics in the first place? Answer - they don't. And that's with monochrome sensors with no OLPFs!!!
Have a look. This was shot at about f/30 with pixels that are about 40D sized:
Ok, this is my last attempt. Words are certainly insufficient, so hopefully some visual demonstrations will clear things up. Some facts:
1. Diffraction limits resolution at narrow apertures
2. Optical aberrations limit resolution at wide apertures
3. The more lens elements, the more optical aberrations introduced
4. The longer the focal length for a fixed physical aperture, the smaller the relative aperture (i.e. add TC's)
Lets assume we have a hypothetical 200mm lens capable of producing a 1"x1" image circle. Lets assume lens is capable of1.97lp/mm in terms of spatial frequency of the virtual image at the sensor, would roughly translate into a 50x50 "pixel" area within which our subject is resolved. Lets assume spatial resolution is not impacted by the addition of teleconverters. Lets assume our sensor resolution is infinite in the context of this discussion, so we don't have to factor in its effects on resolution. We are JUST talking lens resolution in this case.
Our subject is a small moon.
At 200mm without TC's, the moon is 14 "pixels" in size in the center of our frame. If we slap on a 2x TC and a 1.4x TC, our subject grows to 44 "pixels" in size, nearly filling the frame. Our SPATIAL RESOLUTION is CONSTANT, however we are suddenly able to observe FAR GREATER detail in our subject. If we reduce our spatial resolution by 50%, the more magnified subject IS STILL MORE DETAILED than the original, unmagnified subject (an exaggerated example of the effect of stacking on multiple TC's...which at the very least are going to increase diffraction and therefor reduce spatial resolution.)
This effect can be seen below in this simple animated gif (frame 2, unmagnified; frame 3, magnified same spatial resolution; frame 4, magnified w/ 50% less spatial resolution). Note, I've purposely kept resolution the same or lower do demonstrate the effect of, say, magnifying Jupiter such that it fills the frame (rather than being a small dot in the center of a largely empty frame) without changing spatial resolution:
Two TC's are added to a lens increasing magnification, spatial resolution remains constant, yet we are capable of "seeing" more detail in our much larger subject, even at a LOWER spatial resolution. Magnification and spatial resolution are not the same. Magnification and spatial resolution are disjoint concepts that can vary independently. Increasing magnification by adding teleconverters, while keeping spatial resolution constant, DOES increase the apparent detail we are capable of observing...because OUR SUBJECT IS LARGER RELATIVE TO THE FRAME FOR A GIVEN RESOLUTION.
Well, thats the best I can do. If a small animated picture isn't worth 4000 words, then no amount of proof in this case will sway your opinion. I do indeed believe science backs up what I've said here.