As much as it burns us as loyal fans when a player seems to suggest he has outgrown us in terms of ambition and potential, I find it very hard to get exercised about players who are demonstrably "too good" for where we are or where we are going in the timeframe of that player's career. That said, over the last 20 years, the truth is very, very few players or managers have been "too good" for Everton - as their subsequent careers proved.
The obvious one is Wayne Rooney - clearly we were never ever going to be the right platform for such a genius level talent - though I thought he could have given us two more seasons and still been a superstar. The other really obvious one is Romelu Lukaku. He may not have been a roaring success at Manchester United, for various reasons, but he's clearly become a top rank player at Inter and is likely to be a major player in this summer's Euro.
The others that have gone over the years include Arteta and Lescott. Arteta won a few cups and captained an Arsenal in terminal decline. I don't think we could characterise his move as a failure, but it wasn't an unquestionable success either. Lescott won titles at City - but here's the kicker. He should have been one part of the English central defence at the Brazil World Cup. Instead, the man who stayed at Everton was - Phil Jagielka. So, Lescott certainly won his medals, but even they came at a cost as he fell down the pecking order quickly and his career fizzled out at international level when had he stayed he would likely have been with Jags as Stephen Gerrard headed the ball over their heads into the path of Luis Suarez.
Oh.
Anyway, I love the hubris of the players who "think" they are better than Everton but whose performances have, essentially, been central to why Everton "underachieve". I think it's great DCL is showing ambition. If he continues to develop like he has - and we don't - then he will outgrow us within 18 months. If he continues to miss the copious quantities of one-on-ones he has in the second half of this season, he will be very much punching above his weight holding down a position as Everton's number 9.