You write a very interesting post. I disagree in a couple of places, but I appreciate you putting your thoughts down so well.

Mr. Knightley's anger at Harriet refusing Robert Martin is stated in contemptuous terms, it seems to me. That disparagement might be an immediate response to his own mortification at encouraging a scheme that ends in a man's heartbreak, but it is not at first a calm assessment.

I do not see any graciousness in Mr. Knightley's treatment of Harriet Smith prior to the Crown Ball. Can you cite text I missed, or are you going on your view of Mr. Martin in his other dealings?

I still think that Emma and Mr. Knightley have many similarities in their attitudes towards the other's protege (can we call Mr. Martin that?). They both hear good things from principled, intelligent people, and both dismiss those reports for their own reasons. Both of them refuse a closer acquaintance, seeing nothing in such, and have their eyes forcibly opened by circumstances.

Mr. Knightley, a frequent visitor at Hartfield and interested in all that befalls Emma, did probably seek an introduction to Harriet, but only for reasons of discovering whether she was a worthy companion. Once he decides his answer to that, he looks no farther, and has no wish to gather more evidence to see if he was correct. Sound familiar? (He also goes so far as to use personal pressure to try to force Emma to accept Jane Fairfax as a companion instead, despite neither lady showing any inclination for such a scheme, but that is another issue.)

Emma laments her folly that:

[...] prevented [Harriet Smith] marrying the unexceptionable young man who would have made her happy and respectable in the line of life to which she ought to belong [...]
as early as ch. 47.

Emma never comes to Mr. Martin's rescue, but then, Emma never has an secondary motive to learn more of Mr. Martin, as Mr. Knightley does when he makes opportunities to converse with Harriet Smith. I can not disagree that Mr. Knightley, from his dual motives, male freedom and greater experience, moves to acquaint himself with Harriet before Emma tries to meet Mr. Martin, but I admit I am not following your point here. One of them had to be first, and the plot demands that we see Emma's maturation, not Mr. Knightley's. If Emma loses this race, does that not still mean that Mr. Knightley was not already at the finish line when we started the story?