tl;dr- While there's nothing wrong with "supremacy" as a word, the term "quantum supremacy" is a misnomer. "Quantum essentiality" would seem more accurate.
1: "Quantum supremacy" is a cheesy misnomer.
Right now we're in a regime of classical supremacy. This is, classical computers are generally superior to quantum computers in almost all contexts.
To clarify definitions:
Examples of supremacy:
The Supreme Court of the United States has supremacy over legal disputes in the US. This is, even if all other courts in the US rule one way, the Supreme Court can overrule them all in a single decision.
Humans seem to have supremacy over the Earth, as far as animals go.
The "supreme leader" in an authoritarian power structure has supremacy over authority in that power structure, superseding all subordinate leaders' authority.
The Supremacy Clause of the Constitution of the United States asserts that the federal legal structure has legal supremacy. For example, if a city or state law conflicts with a federal law, the federal law wins.
The supremum characterizes the point at which all elements at/above have supremacy over all inferior elements.
If we get to a point where quantum computing methods are generally superior to classical computing methods, such that no one cares to think of classical computing ever again, then that'd be quantum supremacy.
2: "Quantum essentiality" would be more accurate.
Once quantum computers can do things that classical computers can't, they'll become essential to working with general computational workloads. Essential things have the property of essentiality. Presumably we could call this quantum essentiality.
Terminology like this is already used in other technical contexts, e.g. in biochemistry. For example, "essential nutrients" fill roles that couldn't otherwise be filled, so they have the property of "essentiality" in biological functioning.
By contrast, a "supreme nutrient" would be a nutrient that'd be generally superior to all others in a broad sense. So if you're low on Vitamin C? Just eat the supreme nutrient. Low on iron? Ditto. How about Vitamin A? Yeah – you get the picture.
But, we don't have a supreme nutrient because there's no one nutrient that does it all; instead, we have essential nutrients as they're all necessary in the big picture.
That's what quantum computers will become when they can solve problems that classical computers can't – essential, not supreme.
In short, "quantum supremacy" is a cheesy misnomer for quantum essentiality.
3: Regarding the political/politeness concerns..
First, white supremacists believe in white supremacism, not white supremacy. The misnomer may be common in popular media, but.. I dunno. I'm sure all of us hold ourselves to higher standards than that.
Second, I think the worst that could be said of "quantum supremacy" is that it sounds like a cheesy exaggeration that reflects a relatively poor vocabulary. But not bigotry.
But, more to the point, we ought to select our terminology to be as accurate and expressive as possible. So while we should replace "quantum supremacy", e.g. with "quantum essentiality", we should do so for conceptual consistency – not to legitimize misunderstandings.