Exactly this. If you're going to have an evil monstrous race that is explicitly based on a certain real world culture or race, then you need to have actual people of that culture represented as well.
Likewise, the problem isn't putting evil monsters in culturally specific clothing. The problem is that that culturally specific clothing isn't seen on any good/neutral characters as well.
Which, in the case of Eberron not having cultures that are derived from real world cultures, would mean genies and coutals and raksashas and oni are an issue. That means effectively:
1. They can't be part of Eberron, betraying the first rule of "if it exists in D&D, it exists in Eberron". That is especially bad for the raksasha and coutal, as they play major roles in Eberron's history that filter up to the modern day.
2. Eberron would need radical revisions to add Arabian, African, Mesoamerican, Indian, Asian, etc cultures to it's human population. Considering Eberron's map is full, this would mean either adding these cultures to Sarlona (birthplace of humanity, but currently conquered by psionic overlords) or Xen'drik (a shattered continent where humans never existed previously). Or a new continent would have to be added to Eberron to accommodate these new cultures.
3. These creatures can exist, but in some generalized or stripped format. The coutals become some generic celestial, the raksasha is replaced a generic shape shifting fiend.
Either way, in Eberron's case you're talking about fundamental changes to the history, geography and design of Eberron. We're talking Spellplague 4e Realms level changes. It's not a small fix.
Still, considering how WotC has changed 5e Ravenloft and it's current stance on previous cannon, I guess such radical changes to Eberron aren't out of the realm of possibility. I wager a new Eberron book after 2024 might be in order.