Your friends synthetic rope shouldn't be fraying running through a snatch block unless the rope is too large for the block or the block was used before with steel cable and has damage. Synthetic doesn't just fray on a roller.
Synthetic should outlast steel for plowing as it has no memory. That's the issue with steel, it's bending in the same spot over and over with plow use and it snaps. You have some what many do and loop through a block which reduces the sharp bend, prolonging it's life. That other issue both steel and synthetic have is guys that try to lift the plow beyond its stop point, putting stress on the cable and eventually snapping it.
Nothing beats a strap setup, like a boat winch strap or even an old piece of ratchet strap. Damn near impossible to break.