My thoughts and experience around using AI to generate artwork (posters in the case) is to use AI as part of the graphic design process / image composition, rather than just use what it spits out. For instance I plan to use Midjourney to replace my Blade Runner 2049 Savage cut poster, however it will mainly be use for “some” background elements only. The foreground will be a composite of the main characters taken as frame grabs from the source material. Film title etc on top. All composed in Photoshop. I hope that will produce a unique poster, whilst also reducing down the workload.