Yes. Names like dark matter, dark energy, event horizon, singularity are names scientists give things when they have no freaking idea what they are.
And yes heavily invested in fudge factors to make things work. The Galaxy would fly apart without Dark Matter. But they haven’t a clue what and where it is. ( the late Vera Rubin discovered that our Galaxy did not operate as a large solar system but spun like a solid disk and should fly apart with the lack of Mass in the visible galaxy...so they assumed there was unseen mass and called it Dark Matter)
No, they are names given to entities that account for experimental results and observations. The properties of these entities are well-defined so that further tests and observations either can confirm or falsify their existence. Dark matter, for example, is defined to be an entity that interacts only via gravitation and not via any of the other three fundamental interactions (electromagnetism, the strong nuclear force or the weak nuclear force). Since it interacts gravitationally, dark matter must have mass. Since it does not interact in any other way, it must not have electrical charge or color charge. It must not be composed of quarks and therefore cannot have strangeness, charm, topness or bottomness (these are very specific quantum properties that have nothing to do with the ordinary meanings of the words).
The fact is that ALL entities in science are defined in this manner, by inferring their properties from experiment. Just as an example, answer this what is an electron? We can define it only in terms of its mass, charge, spin, etc., all of which are inferred from experiment. We’ve never actually seen an electron or measured one directly. The main difference is simply the amount of evidence we have — there are more observations based on electrons than on dark matter. This is unsurprising since electrons are much easier to interact with. Even if you were sitting in a room full of dark matter or standing on a mountain of it, you’d never notice. Gravity is a very weak interaction, producing noticeable results only when dealing with planet-sized or bigger objects. If we had to rely on the gravitation of electrons, we undoubtedly would know almost nothing about them.
Of course, all conclusions in science are provisional. Dark matter might someday be replaced by a different concept that explains results better. So might electrons, although that would be much more surprising. In either case, though it isn’t true that the name is just a placeholder because we don’t know what it is.
BTW you’re characterization of DM as a fudge factor is dead wrong. The presence of DM was historically inferred from rotational anomalies observed in galaxies. However the other possibility, namely that General Relativity needed to be modified, was also considered. The name given this is MOND (as mentioned in the article). Both DM and MOND have observable consequences beyond rotation of galaxies. MOND actually does a better job of explaining the rotation of galaxies, but none of the MOND models account well for other observations — all are inferior to DM, which is why DM is accepted.
It is possible that a new MOND model could be developed that supersedes DM, but until then DM is the best explanation.