I think it’s a little more subtle than this. What you’re describing would be unsourced content, which is also not allowed.
However, original research also includes cases where a person is adding their own analysis, commentary, or synthesis of ideas based on sourceable material, but beyond that which is published in reliable sources.
So for example, say there are reliable sources describing a species habitat, and then there are sources that describe how those habitats are threatened but without mentioning the original species. But there are no sources discussing that the original species being threatened due to habitat loss. In that case, synthesizing the sources could conclude this, but it would be considered original research.
In practice, you usually have to go pretty deep into the analysis before you end up butting against Wikipedia’s original research policies, but I’ve seen editors do it time and time again and I’ve even been accused (sometimes rightfully) of doing it myself.
A lot of Wikipedia editors are really intelligent and passionate, and love doing research, and it can be easy to get carried away!
I find that if you end up butting up against this policy, it’s often a sign that you have material that could be publishable somewhere else, perhaps an academic journal if you put the effort into it, or at a bare minimum some sort of pop science journal, environmental activist magazine or publication, or even a local or regional newspaper. Then, when the work is published, you can cite it!