"For example slack is an incredibly successful product. But it seems like every week I encounter a new bug that makes it completely unusable for me, from taking seconds per character when typing to being completely unable to render messages. (Discord on the other hand has always been reliable and snappy despite, judging by my highly scientific googling, having 1/3rd as many employees. So it's not like chat apps are just intrinsically hard.) And yet slack's technical advice is popular and if I ran across it without having experienced the results myself it would probably seem compelling."
I really wouldn't judge the quality of some company's technical advice based on one person's experience with their UI. For almost any consumer software that gets mentioned here, you will find some people who love it and lots of others with gripes. And for e.g. Slack might have bad product/UI people but very good infra people. Better to look at TFA and judge it on its merits.
It isn't one person's experience with the UI. It is everyone's. If you don't think Slack is slow then you have forgotten what "slow" means. It is a chat program. It is incredibly simple. It is not doing anything complicated. We have gigabit internet, CPUs with multi-GHz clocks and high IPC rates, NVMe 4 SSDs that load data from disk almost instantly. It should open in milliseconds, not several seconds. That it ever takes a noticeable amount of time to do anything reveals deep flaws in Slack's engineering culture, because it shows they just don't care about performance at all.
If they had "good infra people" then their program wouldn't sit and spin for seconds, ever.
https://www.scattered-thoughts.net/writing/on-bad-advice/