Some general feedback, though:
1. Ethnic studies have not produced any useful ideas. There is a reason why CS, EE or mathematics need to exist since they produce useful ideas. What have ethnic studies produced that has enriched humanity?
Without more context, I can't tell if this is true or not of 'Ethnic Studies', but if I substitute 'the Arts' or 'Culture in general' for 'Ethnic Studies', then I think you might be conflating 'what is useful' for 'what is valuable' or 'what we ought to study'. IMO, I think usefulness is a good measure of how true a claim is, but art and culture don't have to be true in order to be valuable (fiction being a prime example; it is literally false, otherwise it would be non-fiction).
Usefulness on its own can be applied towards different purposes. What we apply it to depends on our values. For example, I value the enjoyment of arts and culture in general. Therefore, even if Ethnic Studies is only similar to the Arts or other forms of cultural study in general, it might still be worthwhile to pursue, just as the arts and culture are in general.
Are you saying that Ethnic Studies doesn't even measure up to something like studying art or culture in general? (Again, this is where lack of country-specific curriculum context is preventing a better reply.)
3. If ethnic studies exist so that members of these ethnic groups can improve, they have failed in their mission. Ex: There is something called "African American Studies (AAS)" in many universities and colleges. However majority African American ghettos still exist. I wonder what are these AAS scholars doing? If AAS is truly beneficial where are their benefits? It's more like placebo than effective medicine.
Are you certain that Ethnic Studies was formed for the purpose of improving members of the ethnic group? My brief skimming of the Wikipedia article didn't seem to agree with that.
4. The existence of ethnic studies result in members of these ethnic groups majoring in ethnic studies instead of something useful which actually harm these ethnic groups in the long run.
This point depends on point #1 being true (and my general objection to point #1 above being answered also). Still not convinced that Ethnic Studies cannot even measure up to something like studying the Arts or culture in general. More background info is needed.