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.
https://en.wikipedia.org/wiki/Effective_field_theory
demonstrably works up to the electroweak scale, which requires an LHC-sized machine to probe.
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?).
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:
https://home.cern/science/accelerators/future-circular-colli...
