In message , Tim Roll-Pickering
writes

Is it me or did someone set out to make the Aldwych branch next to useless
for the main Picadilly line?

Not really ... it was more historical accident. The Piccadilly started
life as two separate lines - one from Brompton to Piccadilly and the
other from Wood Green to Aldwych. Before they were finished, these two
schemes were linked by a line between Piccadilly and Holborn, creating
the first portion of what came to be called the Piccadilly line - the
consequence of this change of plan left the short stub from Holborn to
Aldwych as a none-too-useful branch.

--
Paul Terry