Well even martial arts films have some fantastical elements or characters and people wearing colourful costumes. Some of these aren't even costumes but just kung fu clothing or ceremonial gear. Why couldn't Iron Fist even be wearing that?
And ninjas wear masks. Is that fantastical? What's wrong with Iron Fist wearing one, especially when it was so easy to just reuse Daredevil's proto mask from season 1 but colour it yellow?
Scott Buck must really lack imagination if he can't even manage to make the equivalent of the most basic costume of DD's work for his own show. It's almost like the people on DD and on IF are on opposite ends of the scale. For DD, it's like they were barely even trying and managed to scrape up some crude proto costume. For IF, they tried endlessly and couldn't figure out how to make DD's proto costume work.
Maybe get the DD season 1 show runner or crew if they're having such problems???