"No surprise that monitor speakers with their small cabinets sound clean."
Absolutely. Cabinet problems can only get worse with size.
It’s no surprise that the largest manufacturing cost is usually the cabinet itself.
According to KEF.
"LS50 Meta’s baffle is engineered from an injection-moulded Dough Moulding Compound (DMC), while inside the cabinet cross bracing and Constrained Layer Damping (CLD) combine to deaden internal vibrations."
What exactly is DMC?
Come to think of it:
What exactly is the mysterious material X that Wilson uses for its cabinets?
What about Harbeth flying in the face of fashion with their thin walled lossy cabinets? They seem to be taking a 180 degree opposite approach to those who favour the heavier, thicker and more solid approach.
Current cabinet trends seem to be heading towards a layered approach (MDF or the better HDF).
Sometimes the layers might even be individually laminated - greater stiffness but with an increase of both mass and cost.
It all depends upon exactly where you want to put those pesky resonances.
As the OP pointed out, as long as you insist upon using a box, it will sound like a box.
Some more than others.