In an interview, old Lester even admitted as much, i.e. that
the Sig was crafted to sound like a P Bass because that was a basssound benchmark at the time. It was just supposed to be a bit more variable than a P Bass via the three settings and the extra output jack plus and offer that acoustic note.
I have
never ever said that a good P Bass doesn't sound well! They're just unassumingly ugly, that's all.