Re. Perspective and focal length.Not true, below are crop factors of various sensor sizes:
As a picture is worth a thousand words.
First comparison, 17mm lens and 200mm lens both on same camera from same place and both f8, these are the full images.
Second comparison, same images with the 17mm cropped to match the framing of the 200mm.
As you will see, whilst the dof is very different, the perspective (the size of the various elements within the frame with regards each other) stays constant. The woman, the trees and the jumps are the same size in both examples when the 17mm is cropped.
This is also a very graphic demonstration of why smaller sensors have deeper dof, the second image crop is effectively a small sensor shot with an 11 times crop factor, which still puts it way bigger than P&S's and phone cameras.
FF - 1x
APS-C (Canon) - 1.6x
m4/3 - 2x
Nikon 1 - 2.7x
1/1.7" - 4.6x
1/2.5" - 6.0x
1/3" - 7.2x
1/4" - 10.8x
I believe the iPhone sensor is in the ballpark of 1/3", for example.