Good luck with that one.
As ChaosLord said, it really produces a tremendous amount of overhead.
I don't think they made it purposely so, btw. The sad truth is that 9 out of 10 hardware/software engineers are vastly incompetent. Been that way ever since computers went past the 1GHz barrier (perhaps even a bit earlier)
Lastly. Your statement about the C64 made me choke a little.
The C64 is incredibly versatile. More so with the current wave of new hardware (can you say Chameleon?)
Chameleon is only one major hardware upgrade and as I am aware of it, it is simply another means of replacing the original disk drive, making transfer of games easier to it and being a stand alone commodore 64.
However, major and many different hardware upgrades such as increase of RAM, provide upgrade to the sound and graphics and other upgrades are not as versatile as the Amiga is. Maybe there is no need for it in C64 as there will be no software ever developed for it...but then again it lacks in many hardware upgrade as Amiga does. With classic Amiga if I wish to enjoy using it for more than what Commodore Inc Intended for...I have this option and there is benefit in return because I can enjoy the media of it more than say C64. If I wanted to watch movies in C64 for example I cannot and will never be able to...and if classic Amiga cannot provide that to me (with your argument) at least there is a PPC version of it such as AmigaOS 4 for example, MorphOS or even AROS...heck even WinUAE.
But then again you guys are working hard to convince me otherwise, why? This is all just my opinion on the matter and I love hearing your counter opinion which is what you are doing and I appreciate your input on it:). But this is just what I think on the matter and nothing else.
Perhaps USB on classic Amiga is slow, but maybe I can get something out of it on a 68060 at least.