The power a fusion reactor produces is proportional to its plasma's volume, the losses are proportional to the surface area. We've known since the 50s that if you keep making a tokamak bigger, it'll eventually produce net power, but bigger reactors are also much more expensive to build. Thus you want to make the smallest reactor that will actually work, which is easier said than done. Stronger magnets shrink the necessarry reactor whereas plasma instabilities you didn't notice before require it to be larger. With the trend in magnet advances of the late 20th century, it looked like any breakeven reactor was going to be big, which in turn meant it would take a lot of time to build.

Work on ITER's design began in 1988 and they designed it to use the magnets they expected to have available in 20 years. However less than 2 years earlier, high temperature superconductors were discovered. An incredible amount of progress has been made in that field in the intervening decades that ITER could never take advantage of. This does not mean ITER is useless; it was always meant to be an intermediate stage before a real demonstration plant was built. At the time, it was imagined that this viable commercial reactor would be truly enormous, but now with the much better magnets perhaps it could be the same size or even smaller than ITER. The lessons learned from ITER, such as how to protect the walls of the reactor, will still apply. While some may suggest that ITER should have been scrapped and a new project started that incorporated high temperature superconductors, the fact is there's always going to be technological progress between a project's start and completion, at some point you just have to build something.

There are many proposals out there for smaller reactor concepts which use different approaches. Much of ITER's criticism comes from those who think these small reactors would make extreme progress if they had access to ITER's funding. This belief is unfounded. Tokamaks like ITER are within spitting distance of breakeven, all other concepts are many orders of magnitude away. ITER gets a ton of funding because it has a very good justification for needing that funding, it's a truly massive machine; the only reason to look at small reactors is that they don't need crazy funding to test. Were ITER to lose its funding there's no reason to believe it would be rerouted to these alternative experiments which have not justified that level of investment.

Most of these small reactor concepts are not very promising as routes to real power plants. That's not to say they are not worth investigating, there could be crossover and the technology may find other applications. The skunkworks concept seems especially suspect: it goes against all established principles of fusion reactor design, and that it's being done by skunkworks shields it from any rigorous academic scrutiny - though what numbers they have published suggest they've made little more than a toy thus-far. Realistically, only other tokamaks and maybe stellerators have a serious shot at beating the ITER development line to producing a viable powerplant baring some unforeseen paradigm shift, which is always a possibility but never a good horse to bet on.

It is worth noting that ITER has had some serious delays and cost overruns. This has been true of most large scale international science collaborations of the era such as the ISS and the LHC. While I certainly wouldn't complain if the process was more efficient, the fact remains that real progress is being made.