A torsion box may allow you to use 1/2 inch ply with 1/2 inch internal frame.
An extruded channel can be installed under the plywood as another optio. And can be added later if you get sagging.
The framing you suggest should also work.
My daughter wants me to build her an L shape computer desk with hairpin legs. Simple, easy to build and easy to take apart and transport. She just wants a table and does not want drawers or shelves underneath.
I was thinking about using ApplePly and I’m wondering about whether I should use two layers of 3/4 inch material or if I build a frame of sort underneath it with 2x2”s would that be stiff enough to keep it sagging?
1.5 inchs of ApplePly is going to be pretty heavy, so I’m hoping the frame idea makes sense.