Sorry to be late to this -- I was offline yesterday. They are definitely different wines. Echézeaux is much more varied as a terroir, but generally, I find it perhaps a bit lighter and more sensual than Grands Echézeaux. In contrast, the latter has darker fruit, greater density, has a distinct licorice or réglisse element.
Back in the 1980s, Domaine de la Romanée-Conti had two wines in its line up that were below the others in relative quality -- Romanée-Saint-Vivant and Echézeaux. With the acquisition of the Romanée-Saint-Viant vines in the late 1980s, the Domaine could begin make the changes necessary and that wine soon was restored to its rightful full grandeur. The Echézaux nevertheless continued to rarely to compete for best wine from its appellation in any given year. That situation changed maybe ten years or so ago (sorry, I haven't gone back to check my notes on exactly when) -- I noted that to Aubert de Villaine when we were tasting together and he agreed, explaining that the Domaine had begun to make extra efforts with its Echézeaux.