A - 'As above' -- Incorrect. "Not just X, but also Y" is the correct idiom.
B - Just like president or priest, the word 'buddha' denotes not just the historical figure Siddhartha Gautama, but a type of person, one who has achieved enligtenment. -- Incorrect. 1) "president or priest" is ambiguous here. Are we referring to a specific president or priest? or generally? Not clear. 2) "Not just X, but also Y". Incorrect.
C - The word 'Buddha', similar to the words 'president' or 'priest', denotes not just the historical figure Siddhartha Gautama, but an entire class of people, those who have achieved enlightenment -- Incorrect. This vanishes the comparison that we have created between a particular class of words. Also "those" here modifies people, when really we want to modify "class".
D - The word 'Buddha' denotes not just the historical figure, Siddhartha Gautama, but, like 'president' or 'priest', refers to a type of person, - in this case, one who has achieved enlightenment. -- Incorrect. "Not just X, but also Y"
E - Like the word 'president' or the word 'priest', the word 'Buddha' refers not just to the historical figure Siddhartha Gautama, but also to a class of persons, who have achieved enlightenment. Correct idiom. "Not just X, but also Y". Correct comparison. Word 'president' or 'priest' with the word 'Buddha'. Correct.