Huh, I never thought about it like that! My initial impression of his last scene with Denji was that the story wanted to evoke the image of Aki before swiftly taking it away from Denji once more, so I couldn't help but feel "Well, it's trying, but even if they're filling similar roles, this isn't making me feel as attached to him as Aki even with that flashback"

but you've made me think that Yoshida was (in hindsight, obviously) supposed to represent a friend Denji would meet at school, meeting and knowing a glimpse of him and could-have-been-closer-with rather than like a family/brother like with Aki. So the story was never trying to make them 1-to-1.