Lansdorp does believe mental is a huge part of it, but thats not his area of expertise. He is a technical guy. All great players have various coaches along the way. Sharapova had daily mental training sessions at IMG. Lansdorp concentrated on the technical while other coaches handled mental and tactical and fitness training.
NLB, we usually agree but I totally disagree with your last post. Mental is HUGE if the skill levels are close. Whether its high level juniors or pros, the mental makes all the difference as the skills are close.
Like some said, if you make the perfect technical and physical player they would blow everyone away.....but thats not reality. In real life the skilled players are all fit, have tactics, have technique. Mental is by far the most important attribute to separate the top jrs and pros.