While of course Emma has MOST to learn in the novel I feel that Mr K changes a bit as well. I dont tnhink that his improved opinion of Harriet is just "she's better than Mrs E" which is quite obvious. I think that he WAS unfair and unkind in his outburst that Harriet was "illegitimate and ignorant" and while I can see why he was wary of hte friendship between H and Emma, I still think that it was not THAT bad in itself and that while Emma did act foolishly with Harriet, it might well be possible that H would find a rich husband through Emma's patronage..
I think that on getting ot know Harriet better he DID learn to appreicate her and not just in terms of thinking "she is less vulgar and awful than Mrs Elton".
I believe he grew to understand her and like her better and to realise that she was at heart a good hearted girl who wanted just to be loved and have a safe loving home and be a good wife. (of course perhaps he didn't realise how fascinating he could be himself to an easily led girl!!).
So he changed a bit, being more tolerant of Emma's protegee and feeling a bit guilty that he had been so "lecturesome" to the girl he loved..