Huh, what? That's just flat-out wrong. The CMB is an incredible verification of the standard model of cosmology. It remains our best measurement of the ratio of dark matter to normal matter to date, and it is next to impossible to come up with an alternative gravity theory which fits the CMB without dark matter.
As for dark energy, dark energy had little to no impact on the universe at the time the CMB was emitted, so the existence (or not) of dark energy doesn't change at all most of the behavior of the CMB. What it does change are the details of the expansion since the emission of the CMB, but this just impacts how we perceive it not how it was emitted. So the effect of the accelerated expansion on the CMB is minimal.
Most of the impact of the accelerated expansion comes in with the formation of structure later on. There's a lot of ongoing work to determine exactly how structures have formed over the history of the universe, and that research can give us quite a lot of insight into the nature of dark energy, and can also distinguish between dark energy and at least some types of modified gravity.
As near as we have been able to determine experimentally so far, General Relativity is indeed spot-on. No deviation from GR has yet been detected at all.