It has one parameter. "Particle we can't see" has as many parameters as it takes to model the density and flow of those particles at any given place in the universe.
Yeah and you're still wrong. The comparison is inapt because for all other cosmological phenomena our information is multimodal and this not currently the case for LCDM. Take the argument to the extreme: suppose dark matter has no weak force interaction. It will then be literally impossible to uncouple our observations of dark matter from our inference of it's distribution, and then LCDM is strictly unfalsifiable and may be used to explain almost anything.
I debunked this idea in the last DM thread: https://news.ycombinator.com/item?id=34365591