Independent of everything else, do you find that code review takes more or less time than documenting?

It's hard to say. While establishing such culture, it takes more time (in the beginning) than just writing bad comments.

/**
 @param {object} db database query object.
 @return  {void} no return value
*/
const runDbQuery(db) {
  /* create object */
  let json = JSON.parse(db.query.result)
  if (!json) throw new Error('Error, Parsing JSON failed') // invalid JSON
  doSomething(json)
}

The snippet from above we found last year .... Neither of the comments is useful. The condition is useless because unless JSON.parse() throws, it will always create an object. Surround JSON.parse() with a try-catch block would be the correct thing to do. Documenting obvious facts is as useless as the included error message.

Establishing code-reviews enables the entire team to learn from each other. Eliminate code-smell, fix logical errors, reduces the time to understand other's code. It's not the holy grail but it's better than betting on documentations.