I absolutely agree with you about Nana Visitor's acting whenever she tries to be emotional. I mean that both in terms of when Visitor/Kira has hissy fits (which she does constantly
in Season 1), and when she gets weepy. Her acting is outright bad in either case, every time, and highly unwatchable.
Brooks has the same exact acting problems IMO.
Thankfully, after Season 1, Visitor/Kira has hissy fits/weepy cries far less often, although they still come up from time to throughout the series, and still ruin every scene in which they happen.
Season 1 of DS9 is by far the worst of the series. Every season, from 2-7, has about 5-6 terrible episodes, with the rest ranging from "okay" to "great." But Season 1 has much more than 6 terrible episodes.
Auberjonois' Odo performance gets a lot more nuanced and complex after Season 1. I agree with you that Shimerman is a great actor and that comes across in Quark. IMO Auberjonois/Odo is equally magnificent, but in Season 1 Odo isn't yet defined well-enough for that to come through.
IMO DS9's Season 1 was bad mainly because it was trying to rehash TNG's formula. They stopped doing that after Season 1.