plasma
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According to this article, neutral hydrogen & helium in interstellar gas clouds outweighs stellar (fully ionized) matter around 10:1:
https://www.thoughtco.com/composition-of-the-universe-3072252
And baryonic matter, which is inclusive of stars and interstellar gas clouds, is outweighed by DM by around 8:1 (the percentages in that article are somewhat dated).
Hence the overall ratio of un-ionized to ionized matter, inclusive of DM, is ~ 80:1
Hence an article stating say '99.9% of the visible universe is ionized' may be technically true, but it hides the fact most matter in un-ionized thus not visible.
Even neutral atomic or molecular matter can interact with EM radiation via excited states. The most prevalent re-radiation being the 21cm hydrogen line owing to spin transitions, and lies in the microwave band far below visible frequencies:
https://www.wise-geek.com/what-is-the-hydrogen-line.htm
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...a "preponderance of observational data" on a Mythical substance that has yet to be observed...
My apologies that the following is NOT from wikipedia, so it's veracity may NOT match that of wikipedia...but still a well presented paper in my estimation, Q-reeus :
https://iopscience.iop.org/article/10.3847/1538-4357/abbb96
" Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies "
"Our results suggest a breakdown of the SEP: the internal dynamics of a gravitational system in freefall is affected by a uniform external gravitational field. This sheds new light on the dark-matter problem and paves the way for relativistic theories of modified gravity in the weak-field regime of gravity g
Thanks DMOE for reminding about MOND as DM-free competitor theory. That article is pretty impressive in its support of MOND based on many galaxy RC analyses. However, Wikipedia again:...a "preponderance of observational data" on a Mythical substance that has yet to be observed...
My apologies that the following is NOT from wikipedia, so it's veracity may NOT match that of wikipedia...but still a well presented paper in my estimation, Q-reeus :
https://iopscience.iop.org/article/10.3847/1538-4357/abbb96
" Testing the Strong Equivalence Principle: Detection of the External Field Effect in Rotationally Supported Galaxies "
"Our results suggest a breakdown of the SEP: the internal dynamics of a gravitational system in freefall is affected by a uniform external gravitational field. This sheds new light on the dark-matter problem and paves the way for relativistic theories of modified gravity in the weak-field regime of gravity g10−10 m s−2."
https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Outstanding_problems_for_MOND
It may take a long time till the dust finally settles.
My Bad, Q-reeus!
As I alluded to in my previous Post, I kinda figured that the veracity of anything from https://iopscience.iop.org would not be the equivalent of wikipedia.
So... Again, My Bad!
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No need to feel bad. At this stage it's entirely possible some form of MOND, not the original version though, will eventually win out. If you just read the articles at https://darkmattercrisis.wordpress.com/ it's all but a done deal. My experience is competitor theorists can erect an equally compelling blog site dispelling MOND in favor of DM or maybe some other modified gravity theory. And the final answer may involve both DM and a MOND-type gravity.
At any rate the OP question has been answered in the negative. Visible i.e. highly ionized plasma matter makes up only a small portion of total baryonic matter, irrespective of DM ultimate status.