Currently the font size of a text created using Text Source varies upon the size of the RenderView. I found the reason to be that TextSource defaults TextScaleMode to viewport which scales the text according to the view size translating into having inconsistent font sizes.
In this MR, this is corrected by simply changing the default TextScaleMode to None when using Text Source
I am sure that we favor consistent font sizes, however, it seems that this has been there for a while, thus I am afraid that introducing this change my break something.
The implication of Vicente’s proposed change is that text annotations you have saved in state files of Python scripts will change in newer versions of ParaView. It will be impractical to add backwards compatibility to correctly scale the annotations back to the size you had set in previous versions, but fortunately updating the annotations should involve nothing more than adjusting the font size manually.