“Show watched topics” links to the latest topics with param state=watching and even if there was a way to see user’s latest stream under something like https://SITE/u/USERNAME/?state=watching, it would not be of much benefit since you still wouldn’t be able to change notification level for topics.
It’s only possible to change topic notification level if you impersonate them, hence one solution here would be to impersonate and link to /latest?state=watching when clicking on “Show watched topics” for admins.