I too have many different detail sets for the 1/72 U-boats (say, VIIC or IXC) which I have acquired over the years: Eduard, Yankee Modelworks, U-Brass, AMP, WEM, Modelbrass, Nautilus, Griffon, Schatton, CMK, Tehnoart, RCSubs.
Yes, you could say that most all brass sets are "re-inventing the wheel" to some degree or another. Some detail sets have more accurate constructions/details in particular items than other detail sets; some detail sets have items that are unique to their set and do not exist in other detail sets.
It's really the choice of the modeller as to what s/he wants from a detail set... quality or quantity. That will help determine which set(s) you get.