Quantum mechanics is demonstrable on a lab bench (or smaller), so your counterargument is completely wrong.
Any useful consequence of a physical effect is, in effect, an experiment that could test that effect. So if the smallest test is with a machine the size of a small country, no device using the effect can be smaller.
They’re using big things to do experiments. Maybe they discover some new physical effect. How do you know that that effect couldn’t be demonstrated in some smaller scale experiment after it’s understood better?
Effective field theory is a general approach to integrate out degrees of freedom which are not relevant to the problem at hand. Trivial example: if you are trying to build an aqueduct (characteristic scale: meters and up), you can safely ignore the inner workings of individual water molecules (characteristic scale: tenths of nanometers), or even the fact that molecules exist at all.
In terms of interaction energies, once you have an effective field theory which demonstrably works well up to some scale E, you know that whatever new physics you may find by colliding things at energies larger than E will not significantly affect physics at energies lower than E.
Thanks to the LHC and its predecessors, E is now upwards of 1 TeV, or equivalently a spatial resolution of 1 attometer; a billionth of a nanometer, less than a thousandth of a proton's diameter. Anyone arguing that this still is not enough, and that a larger accelerator may reveal new physics with wonderful technological properties, must be planning to go live inside a proton.
The first working transistor was centimeter-scale, now billions of them fit in that space.
The first useful internal combustion engines were room-sized, now they fit on a moped.
The truck-sized hole in your argument is talking about "the smallest test". First discoveries/demonstrations of interesting phenomenons don't typically happen at the smallest scale (why would they?).
The first working transistors and engines were of the size which happened to be most convenient to work with. They could then be shrunk because fundamental physical limits to their size were far below human scale. Their inventors were neither constrained by nor interested in those fundamental physical limits. They were inventors, not scientists.
In contrast, a particle accelerator like the LHC is designed from the outset to explore physics at a given energy scale at the lowest possible cost. Shrink it any further and it will no longer work. Despite decades of attempts to come up with alternative designs, when time comes to draw up plans for a successor capable of pushing to even higher energy, it's just more of the same:
Any useful consequence of a physical effect is, in effect, an experiment that could test that effect. So if the smallest test is with a machine the size of a small country, no device using the effect can be smaller.