I still think that dismiss per notification could be useful. For example, if I read the reply on my email and I know I don’t need to reply to it, when I come to the desktop, I can still see the “unread” notification. So, I would have to click it to mark it as “Read”.
And yes, adding the same “Dismiss All” button to the main notification panel, per tab, would be ideal.
How about the “View All” button?