Is there a word or expression that conveys this meaning:
A text (and more generally an expressed idea about any field) seems very clear (crystal clear).
But it is clear only because the author has made significant amounts of (re)work to attain this degree of clarity.
The author is able to do so because he has high expertise both in communication and the subject. He is a hard worker who pays attention to detail. He has stayed with the problem long enough and has studied it from different perspectives so now he can give you the great picture and it even seems so simple. Yet if you wanted to explain it to another person prior to his intervention you would have been stuck by the complexity of it all.
This reminds me of Steve Jobs'
'you have to work hard to get your thinking clean to make it simple.'
In Arabic, we use the expression السهل الممتنع that literally means 'The impossible/abstaining easy' to convey this meaning (please do give me a better literal translation). I learned this expression in Arabic lessons: we were describing the literaly style used in animal fables from the author Ibn Al-Muqaffa' ابن المقفع that is known by his difficult to imitate, very simple yet pertinent style.
From the linked wikipedia article:
he achieved clarity of expression by simplicity of diction and plain syntactical structures.