Nope, they are a “range extenders”. It is about a function that the product provides not about its physical property.I think you're reading more in my comment than what is there. Canon is not trying to "con" anyone into anything. They're making decisions based on what they think will maximize their profits. That's why they exist.
That includes being concerned with preserving their reputation as the maker of the world's finest Super Telephoto lenses. That's why they don't want to make it easy to use their products in a way that gets less than the best results for a particular focal length. They'd rather a customer use a 200mm f/2.8 lens than put a 2X TC between the camera and a 100mm f/2 lens. They'd also apparently rather a customer use a 400mm f/5.6 lens than put a 2X extender between a 70-200mm f/2.8 and the camera, even though they would make more on the 70-200/2.8+2X than they make on the 400/5.6.
The "some reason" Canon calls them extenders is because they extend into the specific lenses for which they are designed to be compatible. You can claim that is completely false all you want, but that's exactly why Canon calls them "extenders" in English speaking countries.
Just because another maker chooses to call them by the more generic "TC" does not mean that the reason Canon calls them "extenders" is for any other reason than because they extend into the lenses they're made to work with. Your example of a third party TC with an extension, buy the way, is not made for Canon EF lenses. According to Tamron it is only compatible with specific Tamron lenses that use the EF mount (but that does not make them EF lenses, only Canon makes EF lenses). The vast majority of third party TCs made to work with Canon EF lenses (even those that Canon does not list as being compatible with Canon extenders) have no elements that protrude past the the front of the flange. For my assertion to be, as you put it, "completely false", every single TC ever made by a third party must have elements that extend into the lens attached to them. That is almost entirely *not* the case.
In the context of discussing Canon's APS-H camera bodies, which is the comment you're trying to argue with based on more recent models rather than what was available prior to 2012 when the 1D X was introduced and Canon ended their APS-H camera line, it was the case that their cropped bodies had higher pixel density than their 1 Ds series FF bodies that existed when the 1 D series were APS-H bodies.
Even today, Canon's top APS-C sports body (20.2 MP 7D Mark II or 32.5 MP 90D, take your pick) have as many or more pixels packed onto a 332mm² sensor as the top FF sports model (20.2 MP 1D X Mark II) has on an 864mm² sensor .
Today, the EOS 5Ds and the EOS 7D Mark II have the same pixel density. Putting the same lens on the APS-C 7D Mark II allows one to shoot at 10 fps for 30+ raw frames or to shoot at 10 fps saving JPEGs until the memory card is full or the battery is dead. Try to keep up with that frame rate on the 5Ds that can only go at 5 fps for 14 raw files or 510 JPEGs before the camera bogs down. So yes, there can be a benefit to putting a FF lens on a crop sensor. You can get shot sequences with the faster camera that you can not get with the slower one.
Again, you're arguing with a straw man you created, not what my comment above said.
Nowhere did I say Canon was "nefariously" doing anything to "screw over their customers."
What I actually said was , "In the past Canon has made a few decisions that seem to indicate they do not want to make it easy for users to avoid paying them the "telephoto tax" to get very long reach with less than very expensive high end lenses."
I observed that when Canon introduced the 1D X they reduced the narrowest maximum aperture that would allow AF to function to f/5.6. It seems Canon underestimated the usefulness to many of their customers of making AF available with f/8 lens+extender combinations. Canon heard those customers loud and clear and gave them what they wanted. How is citing that inferring that Canon was trying to "nefariously" "con" their customers?
I pointed out that once Canon heard the complaints from a vocal segment of their customer base, they issued firmware updates to enable AF using the center AF point with the 1D X and the 5D Mark III. That's a far cry from presenting a "... theory that Canon is nefariously limiting AF options." The only thing being blown out of the water are the imaginary arguments you're making up.
The firmware updates that enabled f/8 AF also actually work "at an aperture that they know it
won'tcan work worth a damn at (sic)." You know, with those lens+extender combinations like the EF 400mm f/5.6 L + EF1.4X and the EF 300mm f/4 L IS + EF2X that you claim do not "... have apertures wide enough to result in an acceptable aperture that will work with AF when you put a teleconverter on them?"
Since that time, Canon has introduced several upper tier models that also allow the AF system to function with f/8 lens+extender combos with an increasing number of AF points that function at f/8. I guess that blows your little theory (that Canon knows f/8 lens+extender combos don't work worth a damn) out of the water, huh?
A functional description sell a product better than a physical statement.