Best I can tell is that Starboard is UHMW polyethylene, which is compressible. It's like more dense plastic cutting boards, or more dense milk jug plastic.
G10 fiberglass reinforced epoxy board, aluminum plate, SS plate, or hardwood is a better option for backing plates, in my opinion.
That being said, most deck organizers I've seen are used to redirect the horizontal run of a line, and I don't think they see as much load as, say, the turning block at the base of a mast bringing down a halyard and turning it 90º from vertical to horizontal.