Did you even read the article? All of this is covered.
The question of "what benefit would having a dynamically loaded library give you when each app runs sandboxed" seems to be answered in great detail under "Debugging Info and Consistency" and "Missing Shared Library Features"
The question of "what benefit would having a dynamically loaded library give you when each app runs sandboxed" seems to be answered in great detail under "Debugging Info and Consistency" and "Missing Shared Library Features"