I agree he was unjust to Anne. The conversation you quote from chapter 10 also makes me wonder if Fredrick considers Henrietta yielding to Mary and Anne yielding to Lady Russell to show an equal degree of indecisiveness. IMO they are very different. In Henrietta’s case it’s only Mary, a rather silly person, who is opposed to Henrietta marrying Charles Hayter. “Charles's attentions to Henrietta had been observed by her father and mother without any disapprobation.”