Prevent SharePoint from using custom CSS-classes when using RichText editing

Question

We have a number of Rich-Text fields (multi-line) that users type data into. So they might format the color of the text, the font size etc.

The formatting looks like this in SharePoint:

We have a tool extracting information from SharePoint Online and convert it into a report of some sort. The selected formatting should be preserved.

Our problem is that the applied style is not saved as "inline CSS styles" in the Rich Text. Sadly, a reference to "internal" SharePoint CSS-classes is used, and our external tool has no way to tell what those classes mean.

The HTML created by the Rich-Text editor is this:

<p>
   <strong class="ms-rteThemeForeColor-6-4 ms-rteFontSize-4">​do
    <span class="ms-rteFontSize-1" style="text-decoration: underline;">ubl</span>e
   </strong>
</p>
<p>
   <strong class="ms-rteThemeForeColor-6-4 ms-rteFontSize-4">T
     <span style="color: #ff0000;">his </span>
     <span class="ms-rteThemeForeColor-9-3">is a te
       <span style="text-decoration: line-through;">st</span>
     </span>
   </strong>
</p>

Notice how some of the formatting is done inline - like the #ff0000 color and the underline and strike-through, while others are done using CSS-classes.

The result of not knowing about the internal SharePoint classes is this:

So what can we do to fix this? Can we script/configure the RichText editor to use inline CSS styling always?