Again, the current tax structure really has nothing to do with it.
The OP is about the measurable fact that Democrats (many of them) passed tax cuts that benefit the rich.
Your argument that there is no way to cut taxes without primarily benefitting the rich because of the structure of the tax system is just nonsense. There are more than fifty ways to cut taxes and the current tax structure does not force major benefit to the rich.
Heck the structure can even be changed if Congress passes a law.
Tax cuts for the rich are simply NOT the only alternative, much less the best one.