Not that it would close the gap in any significant way, but you should theoretically combine Lemmy and Kbin as well. And any other app that decides to be an ActivityPub-based link exchange / forum.
Like so many of those sorts of decisions, Digg leadership ultimately assumed - incorrectly, to be sure - that their users would "get over it" in time.
They'd had minor revolts over the 2.0 and 3.0 redesigns, they'd had sitewide discontent several times during the 3.0 era due to changes in the content algorithm ... Digg had weathered several storms by that point, and I think site management simply assumed they would continue that trend.
There's a perennial issue I think for Authorities in that sort of position where you're exposed to so much baseless griping and complaining from the extremely-vocal minority that you need to gain some ability to filter out negativity and criticism, or you're crippled by it. You cannot make everyone happy and only the unhappy people will bother to express themselves, so you learn to filter out the discontent and focus on the theory, on the goals. Many times you genuinely know better than this or that upset user, and you take solace from that. But from that position, it's so easy to then also block out the more important negative feedback, the necessary criticisms, under the assumption that 'you know better' - because that's how it went the last ten, hundred, thousand, times this sort of thing came up.
Which is IMO a lot of what happened to the whole of Upstairs staff at Reddit. They got so used to users complaining and users being upset about this or that little thing that they had to develop a certain amount of resistance to that feedback - but they've reached a point where they're so resistant to all feedback about their site that they wound up losing touch with the site and its users.
I think a huge part of where Reddit went wrong and will continue to is not having and/or listening to people on staff who are skilled and qualified at simply understanding site users and site user culture. So much of their current issues could have been avoided if they had a person in a leadership position, an equal at the C Suite table, whose whole and total responsibility was understanding the users and speaking 'for' them accurately - representing them as if they're stakeholders in the company.
Digg had 40 million unique users per month at its peak. Reddit reached this number on 2012 iirc, almost 2 years after the Digg Exodus. Google search terms are not that reliable for something like this, although they can clearly show trends
It spans May 1 2010 to December 31 2010; the 4.0 redesign launched August 25 of that year.
You can see searches for both sites spike at about that point in the graph - the 4.0 launch inspired a shitton of Digg traffic from people checking it out, and a shitton of Reddit traffic as the users left Digg.
Now we have to get our oligarchs to read a bit more about roman emperors getting killed off by family and their elite guards lol. This insanity has to be cleaned up and itl be their family and guards that do it.