Thank you for your post.
At this time, it is not possible to change the default font size for a field label. You would need to select the field labels that you want to change (either individually or as a group) and change the font size, style, alignment, etc.
I would encourage you to enter this information into our Feature Suggestion web form at:
Although I could easily copy your suggestion and paste it into the form, there are additional questions asked that only you can answer.