What problem does this address?

The impact on clearing a customization on a template or template part can be huge, especially when you put a lot work in building your templates with the FSE.
However, all the work can be deleted with just one or two thoughtless clicks on the menu:

What is your proposed solution?

Add a modal where the user has to confirm that all their work will be deleted. Maybe some additional info text to make clear what impact the clearing exactly has.