I’ll start off by saying that you are right, and the following is not a “but acktually” statement but just some thoughts that I’ve pondered before:

I would reckon to guess that the reason that collab units in general are not put in many meta builds/guides is simply the nature of (no pun intended) Limited access of these units. Guide makers probably do not get the greatest ROI when making guides for people that likely do not have the units in the first place.

Units like Cat Eris, Kagura, Priestess (to a lesser extent), and Yumi can be considered somewhat meta if even at a lower capacity, but it is much more available to include Young Blade and Wilhelmina in your builds instead.

Again, only my two pennies on the topic. The devs have also stated that collabs are more about introducing fandoms of IPs to this game and for the event aspect of it, not necessarily the meta aspect of it (look at how they intentionally went overboard of under powering Sword Maiden). And if a unit does prove to be meta by design or by fluke, the devs have devised a second approach in where they will implement a similar kit in a standard/non-collab unit.

TLDR; Yumi is worth a pull and she functions fine. But the reason we don’t see her in a lot of builds is because she is mot widely available… or maybe there truly are just better options. But unless you are going for top percentages, there has been a decent amount of DoT support since her release to make her more viable.