If I was lucky enough to be in the position of a Rory or a Kyle Stanley I would make the switch but only if I could use only whatever putter I choose.........Rory never should have took the Scotty out of his bag.
Your putter is, IMO , one of the most personalized tools in your bag Almost like a security blanket.
Nike irons and drivers, while probably still inferior to Titleist, can probably be brought closer to specs of the quality of Titleist clubs.
Your putter is more of a confidence thing and you grow to a level of comfort.
Technology wise outside of the ball, [Pro V is superior to anything Nike puts out] Nike may be close but comfort wise and confidence wise it was a bad move to switch putters.
I am sure Rory will eventually figure it out. He is too great a talent