The loss of rigidity from the slots is significant, and it also makes adding a spoilboard more complex — the nicety of the MDF base layer with T-track and filler strips on top is the filler strips may then be easily replaced — doubly so if one uses standard lumber sizes as I did at:
Threaded inserts have the advantage of infinite customizability and I’ve previously opined that if I have to set up a machine again my inclination would be for threaded inserts, but rather than installing an array of them, I would create a master file, and would drill for inserts as and where needed, installing them only at need — that way I’d be sure each insert was used at least once.