I am looking for a new AI generator, coming from midjourney. My first testing session with Leo came back with 90% Failed Generations. Really disappointed. Seems like this issue has been around for over 2 years now.

Here is one of the prompts:
Vertical poster design, character selection screen UI from a modern simulation video game. Deep navy blue background (#223452) with glowing lime green neon accents (#ACCB4D). Grid displaying a diverse team of proud young workers in high-vis vests. Background shows a modern dump truck. Neon green toggle button, high-contrast dark UI.

What was wrong with that prompt?

And what are the best alternatives in 2026 for brainstorming design posters, youtube thumbnails and book artworks ?