yeah that's exactly when strapping breaks down. Doesnt matter what angle the planks run, sheathing ply over the trusses gives full nailing surface anywhere. Saw a guy do diamonds running 45 in a Phoenix sunroom last year, just 7/16 ply and a brad nailer.
For a 15' diagonal layout, strapping gets fiddly. Half your strapping ends up running parallel to the planks unless you do two grids. Easier route: 1/2 sheathing ply screwed to the trusses, then nail the T&G wherever you want. No spacing math. Did this on a covered porch ceiling for a buyer in...
Plywood is worth the premium over OSB for garage walls if you plan on hanging anything heavy. OSB holds screws fine initially but the edge swell from humidity cycling weakens the pull-out strength over time. Plywood cross-grain layers keep it dimensionally stable through seasonal moisture...