"Although literary critics have tended to praise uniqueness in literary characterizations, many authors have employed the stereotyped character...

First, there is a problem with a statement to the effect that "literary critics" value uniqueness. While some literary critics do, others do not. In fact, the notion that originality is a virtue in a literary work is a relatively modern one; in many genres such as oral-traditional epic, originality would be regarded as a weakness. Comedy also tends to be a genre which relies heavily on stereotypes and stock characters.

Wilde's success as a...

First, there is a problem with a statement to the effect that "literary critics" value uniqueness. While some literary critics do, others do not. In fact, the notion that originality is a virtue in a literary work is a relatively modern one; in many genres such as oral-traditional epic, originality would be regarded as a weakness. Comedy also tends to be a genre which relies heavily on stereotypes and stock characters.

Wilde's success as a comic playwright has less to do with his plots or the originality of his characters than with verbal pyrotechnics. Several of the characters in the play could be straight from Roman comedy, with Lady Bracknell taking the role of the "matrona" (strict and powerful mother figure), Lane the "servus callidus" (clever servant), and the two young couples the traditional young romantic lovers. 

Much of the comedy in the play is created by the way in which the characters ironically subvert the stereotypical expectations. For example, the orphaned young hero is a typical stereotype. Normally, one would expect Lady Bracknell to utter conventional expressions of sympathy on hearing of Jack's being an orphan. Instead, she states:

"To lose one parent may be regarded as a misfortune; to lose both looks like carelessness."

Although Cecily and Gwendolyn might appear to fit the stereotypes of the helpless young maidens who need to be rescued by their male lovers, in fact, they turn out to be intelligent, manipulative, and quite determined. In general, the women of the play create humor precisely by subverting the stereotypes of weak, helpless women. Cecily, in particular, rather than fitting the stereotype of an innocent country girl, is well educated and quite sophisticated.