Permissions at product line prevent the ability to deselect weekly notifications for products Merged

Your workaround only works if the user doesn't need to have product owner access at the product line level.  If they do then your workaround doesn't work.  Removing the user from a product owner at the product line leave is a pretty hokey workaround from a users point of view. 

Alternative suggestion, why not default emailing of the weekly summaries to ON instead of OFF for all products that a user is the product owner of at the product line level.  Or allow a system setting to trigger this on or off nature of distribution of emails for all users who are product owners of a product line.   Something to allow product line owners a view into what's happening with those products. 

By default, users who are granted permission at the product line level, will not receive weekly summary emails. For users who you would like to send weekly summary emails to, one workaround is to grant permission at the product level.

We had considered making changes to this feature to allow greater flexibility in weekly summary email permissions at the product line level, but upon a closer look, there are many complexities in implementing this feature. At this time, we are unlikely to implement it, but we will keep this open as we continue to get more feedback.

As mentioned above, the noted workaround will allow you to choose which users you would like to send weekly summary emails to.