Fully agreed that 'extreme diets' aren't at all for beginners, and for at least two reasons:
1) As you alluded to, they simply wouldn't "need" to employ such strategies and are far better served making basic changes permanent.
2) The post-diet phase/transition back to normal, sustainable eating patterns is almost certainly more important than the 'extreme diet' itself and requires some amount of nutritional awareness (that's ideally personalized to that individual).
All that said, I'd still say that some personal experience with 'extreme dieting' is necessary to get one to the intermediate/advanced level in this context. For whatever that's worth.
(And certainly be aware that 'extreme' methods in this context are how eating disorders/unhealthy relationships with food can/do develop)