On a relevant note first plasma in ITER is still 3 years out.
https://www.iter.org/construction/construction
But still if everything worked perfectly I would hazard we would still be at least 20-30 years out of a commercial project that would cost billions and take a decade to build.
ITER has horrific power density, some 400x worse than the reactor vessel in a fission power plant. Given that the non-nuclear part of the a fission and DT fusion plant will be similar, making the reactor itself much larger and much more complex, and therefore much more expensive, cannot be a win. The less experimental follow-ons to ITER (PROTO, DEMO) are still massively too large.
This generic problem with DT fusion reactors has been known since at least the 1980s.
The initial investigations from MAST are encouraging, but we'll see how it goes.
Of course, this stuff will be ready for commercial use in like 2050 assuming everything goes to plan (which is rare unless it's really prioritised like the Manhattan Project, Apollo Missions etc.)
So regardless, something will have to be done prior to then - either we find better energy storage solutions for renewables or we expedite the construction of replacement/new fission plants or both.
For a PWR, this is about 20 MW/m^3 . For ITER, it's 0.05 MW/m^3 and for ARC (2014 paper) it's around 0.5 MW/m^3 .
The scientific work that is planned to be done at ITER has the possibility of proving that nuclear fusion may be a viable path for electrical generation. But it will never serve as a commercial basis for the generation of electricity. Accomplishing nuclear fusion is actually relatively easy. What it hopes to prove is that controlled nuclear fusion can serve as a net producer of energy. A complete success of the ITER project in no way implies that nuclear energy is commercially viable. From a scientific standpoint it is amazing work. From an energy generation standpoint, it's a card trick.
The follow on "DEMO" project will attempt to establish commercial viability of nuclear fusion for electrical generation would commence operation no earlier than 2050.
If clean energy is something we need now, then nuclear fusion is not a viable solution.
That was kind of my point as well, commercial fusion is decades out in the best of cases, thus making the reluctance to maintain and or invest in proven fission technology that much more risky. If commercial fusion was few years out I would be much more sympathetic to objections to fission.