Cannot verify the statement of the questioner.
Like @AlexKemp I cannot remeber having worried about the cursor size. Seemed o.k.
Now, of course, I tested (with LibO 5.0.2) Writer and Calc as well. My result: In Writer the cursor height adapts to the font size. Inside a Calc cell it does, too, but only when shifting to another line. Inside one line it follows the maximal font size occurring in the line. This is the case if the lines are created with Ctrl+Enter, and if they are created by automatic wrap.
Can it be that we have a different understanding of the term “cursor”? Or what?
Best the questioner should attach an example demonstrating the effect (showing it for him).