There is signalling content associated with being at the number 1 bank (and a top group within that bank for that matter; e.g., the financial institutions group

There is signalling content associated with being at the number 1 bank (and a top group within that bank for that matter; e.g., the financial institutions group at Goldman Sachs). If you planned on staying at an investment bank for your whole career then this might not be so important. The majority of people who start these jobs hope very much to jump ship as soon as possible to work on the buy side (hedge fund or private equity), and in that regard the signalling content is very important because there are so many good candidates for any available spots.