If you have a model that explains our observation better, we're happy to hear it.
A working theory is just that. A theory. It's what people came up with based on what they can observe (the funny part is that the same is actually true for all the religious texts that explain how the world came to be. Man observed his universe and, lacking any other kind of explanation, invented some Gods that explain his observation. Sadly, these theories were not improved over time but enshrined as "holy texts").
New observations will be made over time. At least I'd hope so. These observations now either fit into the theory (now that would be great) or they don't. If they don't, it's time to fiddle with the theory. Dark matter and dark energy are indeed a bit of a puzzle since we can observe their gravitational effect, but it doesn't interact with the rest of the universe in any other way. It's just "there". There are actually quite a few ideas what could be behind it, but for a theory they pretty much all lack the "angle" to test them.