After seeing the large train layout my buddy build with OSB, I built one of my layouts with OSB.
I cannot put my finger on the exact reason, but I did not like working with the OSB, and went back to plywood for my next layout.
IMHO, 1/2 B/C plywood is fine so long as you pick good pieces, and frame it properly.
I did another project with OSB a couple of years ago. I found the edges to be very splintery. Had to wear gloves to handle it.