I believe that the Welcome Notebook is the most important friend to new users of Joplin. So, I think having it not be quickly deletable might enforce the idea that users should read it before they ask for help with beginning usage questions here.
It would just be a modification of the current delete prompt with a 5 second timer on the confirmation button, a second button that says Close, and a Please Read Before Deleting prompt.
Personally I don’t like to be patronized by software. Besides I can’t imagine this will stop anyone from deleting the Welcome Notebook and read it instead.
On the other hand I have to agree with you, that most people just delete it immediately on first start and wonder how joplin works.
Maybe some kind of playground / welcome notebook accessible via “Help” would be an option.
That way it would even be possible to show current and long-time users new features.
Maybe it will be possible to integrate some kind of playground notebook resetting each time visited to the current version using the multiple profiles feature which is being in development for GSoC.
I agree with the idea of a “must-read” welcome booknote.
It could appear in the Help menu or below the “About” menu and be called such as “Joplin Basics”.