IMHO It's still faster than most webapps on mobile. I use an old Alcatel with Android 2.3 to benchmark performances on low end handsets and Facebook performance

IMHO It's still faster than most webapps on mobile. I use an old Alcatel with Android 2.3 to benchmark performances on low end handsets and Facebook performances are ok compared to Gmail or even Google search which takes 3+ seconds to load just to display a search box. I think Facebook has managed to do an acceptable job if you compare their app to other web apps. The truth is, the mobile web space is not a good as developers expected it to be in 2015 unless users visit websites with expensive devices, which most of them do not. Making a website responsive , while being an improvement, doesn't make it automatically mobile friendly.