I recall multiple conflicting stories about how this is the future and how this is waste of money on a ill conceived giga-project.
I also recall a skunk works reactor that takes radically different approach (smaller reactors, instead of big) and was supposed to have results if few years.
IIRC, when ITER was conceived, it wasn't a waste of money. They just chose a conservative development path that was expensive but very likely achievable. Technology and theories have since advanced that might leapfrog it, but the project has still contributed a great deal to our understanding of fusion and the engineering required to produce it.
Relevant talk by one of the MIT professors working with Commonwealth Fusion Systems:
Timeline (in case you want to skip over some parts):
00:01:00 - introducing Dennis Whyte, MIT department head for nuclear science
00:04:24 - presentation starts
00:06:00 - identifies breakthrough with REBCO magnets
00:07:25 - explains deuterium-tritium fusion
00:12:30 - basic metrics for reactor performance
00:17:15 - energy output of other previous fusion experiments
00:19:00 - examines ITER and the problems of its approach
00:22:00 - problems solved by high energy magnetic fields
00:28:15 - full scale reactor concept, teardown of REBCO magnets
00:37:00 - design limits and margins
00:39:00 - fixes plasma instabilities found in weaker magnetic chambers
00:40:00 - maintainability, lifespan, component replacement
00:45:00 - solution to neutron damage and energy capture
00:50:30 - cost and profitability
00:54:00 - full graph of field strength vs reactor scale (and thus funding requirements)
01:01:50 - Q&A
01:30:00 - question about the biggest risks
> Technology and theories have since advanced that might leapfrog it
With "might" being the operative word. As long as none of these new approaches has achieved viable fusion (so, more power out than in) I think it's not a bad idea to just continue with the less radical plan that will probably work, even if it is slower.
ITER is research. There are numerous engineering problems yet to be solved, plasma physics, materials science, you name it. Research projects are always a "waste of money" in some way so that particular criticism is neither surprising nor very helpful.
My take on it is that 'it takes two to tango'. Massive investments in ITER send a very strong signal to the market/innovators. And IMHO other initiatives would not have gotten funded if it were not for the trophee of getting it to work before ITER does.
Sort of like the space race between the USA and the USSR.
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.
Relevant talk by one of the MIT professors working with Commonwealth Fusion Systems:
Breakthrough in Nuclear Fusion? - Prof. Dennis Whyte (2016) - https://www.youtube.com/watch?v=KkpqA8yG9T4
Timeline (in case you want to skip over some parts):
A more recent (2019) talk with more numbers and even more confidence: https://www.youtube.com/watch?v=rY6U4wB-oYM