I think it may be more so for logged in users. When logged in, and I go to the homepage, which is essentially an activity feed, it has 93 requests, 4.4MB of resources (1.5MB transferred), and took 7.66 seconds to finish.

In my experience, Goodreads loads slower on a phone than on a desktop browser (and it's only the initial load that I notice being slow). I've long suspected (without evidence) that this is intentional because they nerf the mobile web experience in an attempt to get you to use their app.

I don't use their mobile site, but the android app works really well, and looks great.