The answer to that question is "In Joomla 4 it is, but authors will be able to see unpublished articles by other authors", which we don't want. Therefore we've been working with our custom content table where the primary key is given by id and version number. How should we go about the routing system, in order to have a page for each record of this table? The easiest way would be to make adjustments into Joomla's Content component so to substitute everywhere Joomla-content pages with our custom ones, but that's not possible, is it? Is there some kind of "hack" or do we actually need to create a new component "com_articles" totally adhering to the conventions and structure found in: https://github.com/joomla/joomla-cms/tree/4.1.0/components/com_content ?
if you just want to use different content than the one stored in the com_content tables, why not creating a simple content plugin which replaces the content in the row before showing it?
That way you can use all the benefits from Joomla com_content and show your customized content.
There are lots of content plugins (in the core and in JED) which can guide you on how to do it and this article from official documentation might help (though it is specific for J3, almost everything will work in J4): https://docs.joomla.org/J3.x:Creating_a_content_plugin
Of course if there is not a one to one match between your tables and Joomla article tables, you probable better create your custom component to show this data.