According to me, Momiji was not planned to be released that soon. So they didn't have time to produce scenes for her. They just threw her at us when they saw people complaining + to boost the sales.
Kula and Mai were planned but probably delayed.
Nyotengu and Phase 4 were planned from the beginning but eventually "used" as bonus content. Phase 4 I can understand, Nyotengu not so much as she is part of the franchise now. Maybe TN wanted to make a parallel to Tekken's Eliza who was also a bonus character.
Leon/Gen Fu will (probably) have cutscenes as they were (probably) planned but not prioritized. Plus, they ARE in the DOA Trivia, where Momiji is (still) not.
I WISH SOMEONE COULD HACK THESE 30+ STORY SCENES THAT WERE CUT. SOMEONE.
So yeah, except for Nyotengu who had cool moments in the story, the rest is just... meh. Momiji has none, Kula and Mai (who I don't care about) only have promotional scenes and Phase 4 is not an unique character. Hopefully Leon (and Gen Fu maybe) will have good moments as well. Last time was DOA4...DOA3 maybe? I'm curious because there is so much potential.