When Island of the Giant Pokémon was being conceptualized, Yuyama even toyed with the idea of writing the script for it himself, because head writer Takeshi Shudo was dragging his feet on putting that episode into rotation. Shudo eventually wrote the screenplay himself. #anipoke
Chief Director Daiki Tomiyasu wrote the screenplay for today's episode. This isn't unheard of (Yuyama has a few writing credits, including Ripple in Time, and Yajima co-wrote M21 and M23). I think three episode credits gets you membership in the Japanese Writer's Guild, which has union benefits.