It seems like there are a dozen or more fusion startups that are pursuing concepts that are much smaller than ITER. I'm no nuclear physicist, but it seems like there might be room for innovation still.
Small prototypes don't mean immediate progress in fusion, the original tokamak was hailed as great progress in 1958 and it was less than a metre across.
Until we have perfect understanding of Magnetohydrodynamics and materials science one simply cannot reliably predict the behaviour of completely new devices.
It's like saying a 5nm CPU design is somehow the same as a 32nm CPU, even if they both had the same die size, even those the 32nm versions had far less transistors.
To summarize:
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--> your commentArc is doing what JET and Alcator C-Mod did (with a radius very similar to JET), just with a much more power efficient confinement system, so the input power is lower, and the magnetic field is a factor of 2.6 stronger. The basic physics show that stronger fields actually make the plasma more well behaved, not less, so the major variable vs JET (a proven existing tokamak with Q=0.67) that's changing is not likely to lead to surprising results.