It can go either way. Plenty of sprung set ups out there.
But I tend to agree- little relative motion, yet isolated.
When I reworked the Rega, I have a somewhat massive plinth, but a constrained layer sub-plinth is also added. Each element is on it's own elastomer-coupled layer. Motor, feet spindle and arm.
I would probably keep it simple and have a bolt goung through the two plinth layers and sandwiching the arm board between them.
But the only way to really know is to listen to the final design.