Hello!
Thanks for the detailed comments.
Taking the time to share the context & intent is a huge help and is a great example for others to imitate.
The developers are actively seeking improvements to the Image description parameter.
Until updates are released, there are some excellent tips in this thread:
[Redefine] Image Description Tips
Specifically on navigating the text field, I recommend
- click once to place the cursor,
- scroll to the desired point,
- hold shift, then
- click where you want your selection to end
This works in either direction (up or down) and is a temporary work around to the issue of drag-selection.
Personally, I keep a note open to write and edit my image descriptions, then copy and paste into the text field, avoiding all of these quirks.
Hope that helps for now.
Thanks 
