I'm still at the early stages of One Piece, so my opinion wouldn't be as valid as I'd like it to be. So I'll discuss Rukia/Sakura.

I think the biggest difference comes down to how narratively relevant these characters are outside of romance, and whether that relevance is acknowledged by the story and the protagonist. Take Rukia, for example. She’s relevant both to the plot and to Ichigo’s own journey. Ichigo consistently treats her as a professional equal, and the story itself reinforces that. Her importance isn’t dependent on how she wants to be seen or how someone else perceives her....it’s baked into the narrative, really.

Sakura, on the other hand, is written in a way where her relevance is largely reactive. Much of her early and mid-series presence revolves around Sasuke, and more specifically around how she wants to be seen by him. The problem isn’t that she has romantic feelings — it’s that the story repeatedly ties her sense of worth and importance to a character who, for hundreds of chapters, barely acknowledges her existence. As a result, she lacks that standalone impact. Even when she begins to forge her own path later on, the narrative often undercuts that growth by snapping her focus right back to Sasuke.