The reasons Germany has to keep a low profile in the EU, and about their nationalism are really quite clear.
1. Germany has a very bad
PR problem. WW2 was so horrific, that people forget that German speaking countries also produced Beethoven, Mozart, Hegel and Sigmund Freud. Coming hard on the heels of WW1, which was terrifying in it's own right, it has permenantly damaged the world's view of Germany and the German's view of themselves.
2. RE THE EU: Remember, 60 years ago most of the EU countries were either occupied by/or at war with a Germany that was espousing their own view of a unified Europe. Of course, the philosophy of the EU is hardly that of "Gross Deutschland". But we are talking
PR. If the EU were to have a "German" accent it would never work. There are people in Poland, France, Holland, Greece, etc. who cringe to hear that accent.
4. There is a great deal of collective shame about the war. Even for people who were not alive at the time. Call it the German version of "White Man's Guilt". However, there is no shame in eing a "European". Quite the reverse, it is very forward looking. Being "German" looks back on a past which is not too savory.