They're not random. They are 1) links to the threads I last personally engaged in, on the page of the thread where I last engaged. and 2) they are the fastest way of getting back to the place I want to get to. I don't go to the notifications and randomly click them until something i like comes up. I have a specific page in mind I want to visit and I can either get there in 1 click with the notification or 3 clicks without, assuming I remember to go to the notifications page. Multiplied by the number of times I do this per day. Adding 2 clicks turns into hundreds of extra clicks after a few weeks.
I am not trying to argue that you NEED to bring the functionality back. It is your choice and I have always understood that. But there is a valid viewpoint for these notifications and you are insisting there is NO valid utility for it. That's where I insist that UX principles should dictate this. The ability to turn off notifications already existed in XenForo, and could have been turned off by default first as a half-measure.
With that said, blaming XenForo and not the user is unironically a better way to get the message across, as stupid as that is.