So you are saying superstition in batting position is key to success. Well, if you can bat, you should be able to bat at any position depending on the requirement of the team.
Well if you try something new and it fails doesn't mean you stop trying , do you?
Jason roy is a great white ball opener and england gave him a chance to open in tests thinking he will succeed but he didn't, so be it. trial/errors are part and parcel of anything.
Virendra sehwag always batted in the middle order for his domestic side, but india gave him a chance to open in tests and he flourished.
there are many other players who bat different positions at international level from their domestic side.
root batting at no 3 doesn't make him any lesser batsman than at no 4.
"Superstition" is not the difference between 3 and 4, don't be daft. For starters, on average you'll be coming in against fresher bowlers and a newer ball. Root likes to score quickly and keep things ticking over, much harder against a new ball that is doing more.
Secondly, test cricket is a hugely mental game. You couldn't even begin to count the number of players with great technique who haven't been able to succeed in test cricket because they didn't have the mental side of their game mastered. If Root's mentality is better at 4, which statistics suggest is true, then that's where he should bat.
As for Roy, he might have done well as an opener in Australia in the style of Warner but that's not where he was selected is it? If you couldn't tell that Roy was going to struggle opening the batting in tests in England then you shouldn't be an England selector. Even in white ball where there's less movement on the ball, he nicks through the slips a lot.