Alt Text in Description

Unfortunately no. The description in the image library is copied to the alt text when the image is added to a page, but as it is more often the case that people didn't add a description and the image also is not decorative, we wouldn't want that to be the default. 

However, please do send in a feature request to our support team to add a property to images in the media library where you can mark it unfocused in the library and then that too could be copied into the page instance when you add it in.