What makes you think fusion is feasible at anything less than stellar scale? It's been known about for 80 years or so at this point and still hasn't reached breakeven. No other technology has taken anywhere near that long to even be demonstrated as feasible.
ITER is generally expected to work, even though it's not an economically practical design. Since ITER was designed, better high-temperature superconductors have become available (Rebco tape), which makes smaller, cheaper designs with higher power density possible. Another new technology is FLiBe, a molten salt used to capture the energy from the reaction.
The MIT Sparc and Arc projects are one group's attempts at coming up with a practical design. They seem to be making steady progress.
Powered flight, computation, batteries, electric motors, internal combustion engines, rockets, and a host of other technologies have taken >80 years to become industrially useful.
Confined fusion has been demonstrated at Q=0.6, it just hasn't hit break-even yet which would make it industrially useful. ITER should exceed break-even and DEMO should produce power in 2051.
- Powered flight: from first demonstration to commercial application was less than a decade.
- Computation: I know about Babbage and Lovelace, but from the invention of the transistor to practical computing was years to decades depending on how you count.
- Electric motors: similar
- Batteries: don't know the history, probably they were known in ancient times, but it's not like their development was held back by anything, people just didn't have much interest in finding applications for them.
- IC engines: At most two decades between invention and useful work. But probably less by more reasonable definitions.
- Rockets: Again, depends on what you count as successful. But people had working versions pretty fast.
Fusion is unique in that we've known how to do it for 80 years, spent billions of dollars on it and outside of scientific research and weapons have no real applications for it. The only way to make the timeline for others seem similar to fusion is to stretch the start date back to when people imagined being able to do something, e.g. to put the start date for powered flight at da Vinci, but you could do this with fusion too (perpetual motion machines?) and make it begin arbitrarily back in the past as well.
In basically all other cases of technological development precise characterization of the underlying phenomena to commercial application takes a few decades at most.
Edit: Also, those older technologies had the massive disadvantage that materials were much harder to get and of less consistent quality. Fusion research has basically not had these problems.
