I find it interesting that planning overruns such as this seem to get pinned on implementation, rather than the planning and approval processes themselves.

The evidence is that the time and cost it took to produce JWST are what they are. That planners lowballed these estimates, or that administrators and legislators wouldn't have approved greenlighting based on accurate estimates, speak to failures in planning and administration, rather than engineering.

Much of the planning / large-project literature, which I've studied for some three decades, seems itself to be largely blind to this distinction.

As to many comments found on the Internet mirroring such viewpoints.