Think about it though. Even though Grass Skirts and Spears are used in Africa they have been used as racist totems and proxies to denigrate black people in the past. So even though they are an everyday reality, someone in the West can (if they choose) mean something entirely offensive in their use of these terms. Just as being Black is a fact of life, but someone can use the term black (even in isolation) in a racist way. Just as Blacks are generally poor(-er) most would object to having that thrown in your face on a regular basis irrespective of your personal view of being 'poor'. It is the intent in the offence primarily and the effect of the offence.
Words are not just words. They are meanings. Shake-a-spear said that "A thing is what it is not what we call it" and we would do well to remember that. Grass Skirts et-al may be facts of life but in the wrong hands they can be used as "offensive facts". See how quickly 'Pepe the Frog' has been fashioned into a perjorative.
A movie is not like life where the full picture is composed on a myriad of experiences to form a tapestry of nuance and experience. A film is cast in a die once (most of the time) and from that point on is an indelible message to the world. There is nothing wrong with showing blacks in Grass Skirts but there is something wrong with having a preponderance to show them in them knowing what we know about the shared cultural backdrop that we all share. And here we get onto the fact that skewed perception (even by a little) skews group phenomenon massively where the results of independent decisions are amalgamated at group level.
Likewise it is questionable to show the negative results of your actions in a positive light for you. A man might be poor and that might be a fact but Riefenstahl-esque imagery of this might be questionable if you are responsible for his poverty.
And finally remember what makes an insult an insult. An insult is a shared phenomenon.
Remember Tin Tin and Tarzan. Remember the role of white surrogates in those older tales of darker, dangerous regions on earth and ask why the MCU chose to open the trailer with two white surrogates. This IMO is the biggest sign that the MCU are NOT as blind to race as some would believe and that they will change their imagery to keep their audience (even the racists ones) on board.
Read this:
Lead You Can Relate To - TV Tropes