Agreed on Diona, I've found her awkward to use, plus I find her character to be irritating, but I'm sure there's situations and character lineups where she would be useful. I never really used Xinyan after pulling her, but that was more due to having better pyro characters. The only 4 star that I don't have is Beidou, but I can see how she would be interesting to play with her counter style.
I tend to use Xingqiu or Mona for hydro in team comps, but Barbara definitely has a lot of utility. There's a couple of characters that I used a lot during the early portion of the game that I've gone away from, but that's due more to wanting to try something new rather than those characters being "bad". This is why I would pull for Rosaria: I know she's not going to be all that great, but it would interesting to try a new character. In addition, outside of Xiangling, I don't have any other spear characters, so that would also be fresh to me.