It's very telling about your own state of mind, that you think your understanding of the meaning of a term deserves recognition over that of an established authority of close to 200 years (founded in 1831), such as Merriam-Webster.
I must admit there does appear to be a bit of a gap in building this definition by MW.
Nationalism/Nationalist have definitions that are not predicated on race. If a person is of X race and of a nationalist mindset would they be, by default, considered racists that see their race superior? Is it in fact possible to be an unabashed nationalist and not be racist?
The MW definition seems to assert it is essentially impossible to simultaneously hold a strong nationalistic attitude and not also consider oneself racially superior. Is that what you're seeing or do you have a different interpretation I'm missing?