Text web part - legible?

How can I style the Text web part on a modern SharePoint page (O365 cloud)?
At issue is the text legibility- the weights are too extreme on both ends. 

Header font-weight 100 is anemic- the lack of contrast makes it harder to read at any font size. 
It makes the bold header font-weight 700, already too heavy, even bolder. 

I cannot find one instance of a similar styling in any of Microsoft's documentation. 
For instance, even Microsoft's Writing Style Guide uses 400 weight regular and 600 weight bold. 
One would expect a text web part to be more legible- at least as legible as the volumes of online Microsoft documentation. My head of platform solutions insists we cannot style web part. 
Is there something we did, or it is like this for all O365 cloud?