You can click "export to markdown" on a notion page, you can click "import from markdown", but those two markdown dialects are totally incompatible. Most of the time notion can't even read what it exported.

The notion web editor for me has very noticeable lag, so I really want to just be able to write some text somewhere to represent a notion table or whatever, but there's simply no supported way to do that I'm aware of.

I mean, it's fine, using a i7 core at 100% at all times just to produce text at a 2 second delay is totally fine for a text editor, I'm sure notion's doing its best.