It's a double edged sword. There was no functional script for Iron Man, a point which Jeff Bridges nailed home because it was the first project that he signed on where he wasn't able to read a script, just a synopsis of his character.
The film turned out great because of the great improvisational skill of Robert Downey Jr. that held the film together.
On the 2nd film they actually intentionally tried to do the improvisational thing, and in large part it backfired, although the film was still very successful, but not among the top MCU films, or even as good as the first film.
With this film, not having a script will be a disaster. You don't do that to young and up and coming actors, and the film will suffer as a result.