Doubt this will convince onebrow...
That's how it is used by people who stody the phenomenon. Dictionaries are great for looking at popular conceptions, less so if you want to discuss concepts in detail. Also, there is nothing in your definition to indicate it is an individual belief, as opposed to a cultural belief (that is, part of the milleu of beliefs associated with the members of a given culture).
That would be a great argument if the dictionary were somehow out of step with scholars of racism, which of course is not the case.
According to the US Civil Rights Commission, Racism is any
action or attitude, conscious or unconscious, that subordinates an individual or group based on skin colour or race.
It can be enacted individually or institutionally.
https://www.usccr.gov
This commission includes Abigail Thernstrom, Adjunct Scholar, American Enterprise Institute, Peter N. Kirsanow, Corporate Advisor in Public Policy and California State University Trustee, Gail Heriot, Professor of Law, University of San Diego, Todd F. Gaziano, Senior Fellow in Legal Studies, The Heritage Foundation
If you want to argue that this is just political, check out their web site, the commission is a mix of independents, republicans and democrats.
If you want, you can easily find dozens of other scholars or racism who us a similar working definition, such as this one
https://academic.udayton.edu/race/01race/race08.htm