you are a computer scientist and obviously you are viewing it from a software-focussed point-of-view.
i have no idea of most of what you mentioned about the architecture, etc.
what i can tell you, as a "common-sense n00b" - is that the Pi uses 'brains', while the Uno uses 'brawn'.
the Pi has processing power and can perform intense calculations say for video graphics but run any currents beyond (5-10 mA ?? -cmiiw-) and it'll get fried.
the Uno has "electrical control" and can switch circuits on and off - even mains electricity via relays or transistors, but it certainly can't do much image processing, beyond some lesser resolution images, say 320p ?
Your question is;
I want to know the difference between arduino and pi.
and then say;
Please dont start off by telling pi is a processor and uno is a microcontroller
and yet - that is infact THE DIFFERENCE !
you should specify what exactly your parameters of comparisons are if you want a response beyond the obvious.