I like the way Fi talks & her voice, but shes incredibly annoying. The dowsing method & her captain-obvious advice beep constantly so u have to activate her. I also like the way Navi talks & her voice. Altho she is annoying too, she isn't required to listen to her as nearly as much as Fi. I like Navi better that Fi, but only because of her persistant advice. So yes, Fi is the new Navi mostly because Fi is more annoying.
But Fi's only reason of being created was to help Link, so its somewhat understandable that she trys too hard to help. Navi was sent to Link by the Deku tree to help u, but for all we know, he could of picked some other random fairy to help link, leaving her unnamed. What I'm trying to say is both of them were suppose to help Link, but Navi had a choice;for all we know she could of had a life...but I should probably stop my random babbling cuz this is a bit off topic.