I liked the character Tasha, I thought she had a very interesting backstory, and I like what she might have brought to the show. But I have to agree that Denise Crosby was not the strongest actress out there. I guess I didn't see her enough to say definitely "She was bad," but I think it is fair to say that she had some decent opportunities, and she nonetheless didn't shine, for what reason, I don't know. Yeah, "Code of Honor" was a horrible episode, but it was made worse by her acting, which just made me cringe. And she made me cringe in "The Naked Now," too, and even a little bit in "Encounter at Farpoint."
I honestly cannot remember a single episode in which Yar was featured where she did what I would consider a thoroughly good job, except maybe "Yesterday's Enterprise." But even there - and I saw this episode just a week or so ago - well...she did OK. She did a competent job. But why is OK and competent the best she could do even in a well-written episode?
Now, she might have gotten better. I mean, several of them did - Marina Siritis, for one, who started out perfectly wretched, thanks to perfectly wretched writing and a fondness (hers or the director's - who can say which?) for overacting emotional moments, and what did they give poor Deanna in the beginning but emotional moments? So I would have been glad for Yar to stay if Crosby got better, or was allowed to get better, whichever the problem was. But if she wasn't going to get better...well, I think we made out great with the cast we ended up with.
And I also agree with those who said that if she was going to leave, having her die in the line of duty was a very powerful thing to do. And just what I would have expected from Tasha, actually.