@wingardiumleveosa I think it really comes down to "hours spent". It takes me roughly a week to write and edit a chapter, sometimes even longer. In addition, I have a lot of help from a friend who beta reads every word I write (she's super professional and thorough with her feedback, so it helps me a lot in the development process. And just as an example, in some of the tougher cases a chapter needs four to five iterations between us alone to get it to a working level).
Other than that, I delete roughly 40-50% of what I write, so I need to write about 3k words to get to my usual 1.5k word chapter length. Personally I found that deleting a lot of what you write helps to focus the chapter on what is important and it really helps smooth the transitions.
After the “delete and replace” marathon I usually read my chapters out loud once (or have them read to me by the "speech/voice function" of my laptop). Hearing what I’ve written usually helps pinpoint the odd parts and smooth them out.