“Niche” is defined by Merriem-Webster as “a specialized market”. Somehow, people managed to replace it with the word “irrelevant”, which is defined by Merriem-Webster as “inapplicable” or, as an antonym to “having relevance”, therefore meaning “not having practical and especially social applicability”
I NEVER would equate “niche” with “irrelevant”, because that is ridiculous, and demonstrates lack of literacy.
There is no school that is more “niche” than small engineering/tech colleges, because the VAST majority of students pursuing engineering degrees are applying to, and attending, large research universities. Does that mean that these colleges are “irrelevant”?
Then there are, as I mentioned, service academies. These are the nichiest of niche schools. Only a very certain type of high school graduate applies to a service academies. Are they, by any understanding of our world, “irrelevant”? That is just plain silly.
So no, “Niche” is not a synonym of “irrelevant”