The only reason why I thought Discovery would be done after Season 4 was just the amount of Trek that was being planned now. I mean there are currently 5 shows that are (or will be ready to) airing this year with a few more in development. However, with that said, the Zora plotline has actually changed my opinion on Season 4 somewhat to the point where being cautiously pessimistic has turned into being cautiously optimistic for the Future of this series. If they keep up the quality of the last two episodes (And Season 2, which before Control became the main villain was probably my favorite season), then the future for the series is looking bright.
I totally get that!
My stance was pretty much... right when the fourth season was premiering, I figured 90% odds of renewal. Which is practically a lock. Once I saw where things were going for Tilly, and as the weeks rolled on by without news of renewal, I kind of lowered that down to around 70% instead, figuring that maybe the mothership show was branching out into a spinoff or two.