"Dark energy" isn't that contrived. When Einstein formulated GR, he showed that when you set up the theory, there is an additional free parameter. People assume

"Dark energy" isn't that contrived. When Einstein formulated GR, he showed that when you set up the theory, there is an additional free parameter. People assumed that it was zero, but there was really no empirical reason for this. But it's just as much part of the equations of GR as matter-energy is. If a dark energy had been not been allowed by GR and still been observed, then the hand-waving would have started.