When writing longer things on either, I find myself firing up vim to copy paste afterwards, just because it's impossible to get into any kind of flow in these apps.
VS code also falls into this category by the way, albeit less severe.
For notion specifically, the total lack of keyboard navigation within a page (PgUp/PgDown, Space, Shift+Space, nothing works!) as well as the fact that wherever I click I will make immediate changes to the document (even if I just want to deselect some text or so) just makes the editing hugely frustrating, slow, and anxiety-inducing.
Seriously, if one day I wake up and write my boss that I'm outta here, notion and slack (and asana...) are way up there on the list of reasons.