"All putts are straight." What that really means is that golfers should always start their putts off on a straight line, even if the ball breaks thereafter.
Even a cut stroke that initially imparts cut spin to the ball has to roll over the ground, and this rolling washes the cut spin out, so the ball ends up rolling in only one direction anyway. The real issue is how best to start the ball rolling on the line you intend R11 Driver to travel on, consistently.
Physics teaches, for a slab of metal such as a putter head to send the ball rolling on a straight line, the fewer variables the better.. Ishiner