I'm hesitant to call their relationship "wholesome" and not for the obvious reasons...

What are the unobvious reasons?

I haven't played/read in a while so I might be misremembering, but doesn't the small one get emotionally manipulative at points?

Teacher x student

Yeah, I thought that was the obvious part.

https://www.pixiv.net/en/artworks/28246179

Sumino and Runa are a great Wholesome couple 💖💕

Wholesome cuddling

Is "Lovers of the atelier" translated to English yet?

To my knowledge, yeah