No, your assumptions of the nature of dark matter have no basis. All that is known is a lot of mass is missing.
This discovery suggests that what was assumed to be massless in fact has mass. Whether that will be sufficient mass to fill the arithmetic void remains to be seen.
Your assumptions about my assumptions have no basis. There are multiple lines of evidence for dark matter. An obvious and classic one is the rotation curves of spiral galaxies and the velocity dispersions in elliptical galaxies. They show big mass concentrations in and around galaxies that are not consistent with the distribution you can infer from the emitted light.
Neutrinos are known to have mass, and known to have very very little mass (cosmology and the distribution of galaxies in the universe actually give the tightest constraints). Particles without a lot of mass given even a tiny amount of energy will go very very fast, and you can't make them stay in a galaxy long enough to hold the galaxy together. Worse than that, we have pretty good ideas about how structures form in the universe (based on very uncontroversial gravity and big computer simulations) and you can't get the observed numbers and distribution of galaxies just with the known amount of ordinary matter plus neutrinos within the mass constraints we have for them.
It's not just that we know matter is missing. It has to broadly have certain properties to work right - it's a very big 'broadly' but it excludes the kind of neutrinos in question.
