"Hence the paradox: how is it that a team of brilliant senior engineers need 6 months to clean up after that one early programmer’s weekend kludge job?"
I don't think things happen quite like that - what I have seen happen is that a "weekend kludge job" becomes the foundation for a lot of subsequent work and the "kludge job" sets the so after a year you can have a vital production system that has been extended and "improved" in a completely ad-hoc fashion and it's that that takes a lot of effort to reverse engineer and structure properly.
In my experience it is really difficult to raise the quality level on a project once it gets going - thing generally only get worse as external things start to impact (timescales, scope creep etc.). The only way things seem to keep high quality is to consciously start high and fight to keep standards high - which can be pretty difficult.
I don't think things happen quite like that - what I have seen happen is that a "weekend kludge job" becomes the foundation for a lot of subsequent work and the "kludge job" sets the so after a year you can have a vital production system that has been extended and "improved" in a completely ad-hoc fashion and it's that that takes a lot of effort to reverse engineer and structure properly.
In my experience it is really difficult to raise the quality level on a project once it gets going - thing generally only get worse as external things start to impact (timescales, scope creep etc.). The only way things seem to keep high quality is to consciously start high and fight to keep standards high - which can be pretty difficult.