Vi(m) is not just a set of key bindings. It is also a philosophy of text editing that is much more integrated with the command line. You cannot replicate it entirely in other editors.
It may be fine for a very casual vim user who wants to switch to emacs but it's too confusing for a vim power user. There are subtle differences that disrupt the flow of my muscle memory. One such example is the }{ forward and reverse paragraph motion. In vim, this is perfectly predictable and delineated by empty lines. In evil-mode, however, it's hooked into the major mode, so it's always changing behaviour as you switch between different file types.