This is an interesting take. I think one of the differences is that there are a bunch of posters missing and there is not really anything, right now, drawing in new visitors. I'm assuming football season may change some of that, but it's going to take some creative and talented posters to bring that kind of draw again. Some of the most creative/talented posters on shaggy aren't posting the same kind of content that they did in the past. My opinion isn't that it is trying to hard, the content is just not what it was.
You could also argue since Shaggy was torn away, that Surly is supposed to be a replacement. Why should it have its own identity?
And since none of that is really about Tapa, I'll post a Tapa comment here. I never use it anymore because the mobile version of this site is easier to use. For the folks who posted lots of gifs and pics, that's probably not true, but as someone who mostly lurks, I hate the way Tapa works now for Surly compared to the way it worked on Shaggy.