It is evident, in spite of his [Edward’s] frequent attention to her [Elinor] while she draws, that in fact he knows nothing of the matter. He admires as a lover, not as a connoisseur. (Ch. 4)

Good point that the word strikingly was also used (Ch. 1) to describe Marianne and Mrs. Dashwood as alike and I agree with your evaluation of its usage—brilliant is right. I completely missed it as I did that “however disregarded before” illustrates not only does Willoughby easily take up Marianne’s opinions but he may be completely ignorant of the subjects but what she has exposed in her raptures. It seems that Willoughby often admires as a lover, not as a connoisseur. (:D)