If he goes to everton he can kiss his 100% guaranteed to be england #1 keeper spot goodbye. Maybe he was better a few years ago and has gone down hill, it happens, look at iker casillas he was unstoppable for so many years then just lost form a few years back.
Every goalkeeper will have their peak and soon after that their form will gradually gets lower , it is not really a problem because he is still much better than most averag goalkeeper on the premier league. Sometimes it is not about goalkeeper alone, if the defenders are bad then it will makes the goalkeeper looks bad
Yeah i think joe hart career has out from the peak since he has made many blunder last year with manchester city and england. some people said england lose against iceland because he made a bad blunder.