SVG vs Flash
Flash has a nice and easy editor, while inkscape is nice it's not as powerful(not in is own fault but because the language wasn't designed for the use flash is used):
- With the actionscript language right inside the editor it is arguably more visual(thus much more comfortable to do things in)
- Flash has built-in animations(using frames and layers) while with SVG you have to use scripting just to get the just animation not to mention buttons, and other GUI elements in flash.
Thus a developer would have to do a lot more work to create something in SVG, and that is just the graphics stuff.
So you can look at SVG as a small part of flash which has much more to offer, and that is because SVG was designed to be viewed in a browser and animations were only added later on(as far as I know).
About Canvas and SVG
I think that SVG and canvas both have their strengths and weaknesses(canvas needs redrawing) so no comparison there, they are two tools for different tasks.
The faults of SVG might be because of not being supported in IE for so long, but from what I think it is because SVG was not designed for the tasks Flash was(displaying animations) but instead it was designed for displaying Scaleable Graphics.