Congratulations: You just killed the word.
Words are useful to the extent they allow us to talk about things, and that involves creating words to describe differences. If you say a word applies to literally every member of what you’re talking about, it’s worthless. You killed it. This is why specialists in a field come up with jargon: Not to keep people out, but to make sure their damned words don’t get killed.
Now, in real-world talk, utopians are the people with grand plans. Utopians have some idea for reforming the world and will work towards that idea in their politics, and have a distressing tendency to see everything in relation to that one idea, such that all issues become purity tests, as in, you can’t be a real supporter if you don’t think this way on this issue, even if that issue has no bearing on the big idea.
Anyway, centrists are not utopians. Centrists want to solve immediate problems with good solutions, which does involve looking down the road to see the likely outcomes, but they have no huge long-term plan. Centrism is not utopian because of the converse of the purity test paradigm: Centrists are willing to compromise, which means they’re able to govern. To be clear: Governing is defined as getting policy accomplished when you don’t have dictatorial power. Pinochet didn’t govern. Mao didn’t govern. Stalin didn’t govern, once he had full power. Hitler set up pointless political bickering in the serpent’s nest he called a government, but he most certainly did not govern.
Therefore, the center is where the action is. It’s where policy is accomplished, and where effective change happens. To a utopian, it is where dreams go to die, and given how many utopian dreams turn out to be nightmares, that is a very, very good thing.
Conservative utopians are reactionaries, whose grand plan involves undoing social change. Most or all GOPpers are reactionaries to some extent, given that the official Republican Party platform involves undoing social change such as abortion rights and GLBTQ+ rights and so on. Centrist conservatives are Blue Dog Democrats, willing to work within the system as opposed to holding dogmatically to positions which have no chance of passing in the system as it is.
And that’s the big point: Utopians demand that the world come to them, centrists are willing to work to move the world to a better place.