I dunno, having Yar's baby momma show up and drop off a kid would have been a challenge to write in the late 80s / early 90s.
VindictiveJudge
Something I would have liked to have seen is Vidiians being assimilated by choice on the basis that being part of the Collective had to be better than suffering from the Phage. Instead of them just being enemies, they should have really leaned into how horrible it would be to live with that plague hanging over their heads. It's also implied in an episode or two that there are uninfected populations somewhere, probably under quarantine, which would have been interesting to explore.
They didn't want to fire her, but she did want to quit. She wasn't happy with the direction they were taking her character. I wouldn't be surprised if she also had issues with the same guy McFadden did. Jadzia was killed off because Berman wouldn't let Farrell switch to being a recurring rather than a regular, which may be what you're thinking of.
I was thinking maybe a seahorse kind of thing.