@Gildaniel, thanks for your suggestions about the default text size of dimension lines, except that the two images you showed over-exaggerate the problem. In a future version, I could try to compute a different text size according to the place it will occupy along the line, propose a default size in the preferences or add a modification pane for selected dimension lines. But as these dimension lines are permanent and printed, I can't change their size according to the current zoom factor like for temporary dimensions, otherwise this would break WYSIWYG (What You See Is What You get) in the plan view.
In case you didn't know, note that the Enlarge / Decrease size menu items will affect all the dimension lines and other texts selected in the plan, so you can select more than one line to change its text size at the same time.