For me, Substack has a reputation problem. All Substack's I've seen shared (on HN) have spouted outlandish claims and had zero (or little) "evidence" to back their claims up. Of course it's just a platform and it is probably made up of some great content too, but the bad content has turned me off to the platform. So I guess none here as well.
There are a lot of wannabes on Substack. There are wannabe "journalists" who don't leave the house and wannabe philosophers who don't study philosophy. There are lots of tech and VC types like PG who are nowhere near as interesting as they think they are. Despite all these wannabes, there are probably 30 or so high-quality substacks that are actually worth reading. I wouldn't dismiss the entire platform.
This was a point made as well on the AMA for Substack, but it wasn't really addressed. The low-quality "journalists" reduce trust in the platform as a whole.
I don't feel like Substack is doing enough here to combat rampant misinformation and low quality "journalism." It on the platform to show me that it's not just filled with conspiracy theorists and low quality trash. And so far I don't see that and will avoid Substack just like I avoid Reddit alternatives (for instance) that champion free speech and end up as cesspools. Plenty of other places to get the same type of information out there that you don't have to tiptoe around the garbage.