Despite this both France (which has just finished building an EPR) and the UK (which is building one right now) are doubling down and launching new projects to capitalise on the knowledge gained.
In France all historical reactors worked so well that we did not feel the need to build more. This lead to talented engineers going to retirement without having a chance to pass on their knowledge and experience, causing cost overruns on the new constructions. This is not inherent to the technology itself but a symptom of our decision to put it aside for a while. As an example when I was in engineering school I remember being told “don’t do a nuclear physics major there is no job for that in the future”. Not easy retaining excellence in a field when that’s what you tell your children. All the dude that went there anyway are in very very high demand today, as you might expect.
The new generation of reactors is more complex, mainly because of additional security and reliability requirements, which is a good thing. Those are certified for a lifespan of 60 years and costs are computed on that base. Some old gen reactors in the us are looking to extend their lifespan to 80 years. It’s extremely likely the new - safer - reactors will be able go beyond that, reducing the MW costs compared to current estimates.
We are slowly re-learning to build reactors, and mastering a new technology at the same time. The more reactors we build based on that experience the more that initial cost will be distributed.
There is nothing underwhelming in what was delivered; the process to get there was, but we will get better at that.