Did you create these annotations in ArcGIS Pro?
Solved: Dimension labels in ArcGIS Pro - Esri Community
related issues regarding font size and when dimensions were created
I've added it as an ArcGIS Idea here: allow dimension feature class property changes AFT... - Esri Community
please vote it up!
I have this problem. I've checked the dimension style properties, line widths are 0.5pt, text height is 10pt & arrows are set to 12pts. But no matter, the entire thing, lines, arrows, text and all is about 100 times larger than it should be for no apparent reason. I've run out of sub-menus to dig through, where might it be getting this giant size setting from?