Leave it to HN engineers to hand wave away going 10x over budget and a decade late.
Your comment is really frustrating. few people in this life can do something that was never done before, much much fewer on this scale, much much much fewer with such impact on science and humanity.
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.
20 year project? Dies in committee.
Welcome to politics.
All I'm saying is there's room to improve. JWST would be a monumental success for humanity even if it launched 20 years late.
https://en.wikipedia.org/wiki/Development_of_Duke_Nukem_Fore...
"The video game Duke Nukem Forever spent fifteen years in development, from 1996 to 2011."
So you would have to do that again basically or come up with another mirror design.
I am sure they have learned alot from building JWT, as they certainly learned a lot from building Hubble or the space shuttle. I don't think that knowledge necessarily transfers forwards to make the next project easier.