It took more than 300 years to build the cathedral [1] in my home town (albeit with a 60-year pause in the middle). So indeed it might take another 4 or 5 generations to master nuclear fusion, but I see no issue with that. We should not shy away from starting projects that we won't see any benefit in our lifetime.
But of course, it also means that we should not rely on nuclear fusion being available in the short term...
The linear model of time estimates here work well for cathedrals but not necessarily for scientific and engineering advancements.
For a Cathedral, you have a general idea of how long it's going to take (at least finite) and know that every piece of material added onto the structure is going to move it closer to the end goal.
For things like fusion, anything beyond say 20 years is basically a bullsh_t speculative guess that sounds better than "we don't really know whether this will even work out in the end". It doesn't really matter whether it's 30 or 60. The real question is whether the number is finite or infinite.
I suspect there was a lot of inceramental value to be had while the construction was ongoing. A cathedral doesn't need to be 100% complete to use as a house of worship, an inspiration for the community, a display of wealth and soft power, and so on.
Fusion hasn't really produced much utility at all so far, aside from some interesting discussions.
Are you trying to argue therefore we should stop or something? There are countless areas of research and activities we do as humans that offer virtually no tangible benefit to society.
It seems to me that fusion is unfairly criticized because there is an obvious end-goal.
If you never stop working on some creative art project it's never finished, your endless cathedral build has nearly zero relevance to nuclear fusion producing electricity for consumers which would be a definitive "delivered" goalpost, after which any further developments/improvements would just be optimization iterations.
But of course, it also means that we should not rely on nuclear fusion being available in the short term...
[1] https://en.wikipedia.org/wiki/Metz_Cathedral