You made me think of something interesting. My 4 hours NEVER happens and I'm in a cube-farm/closed space. Interruptions happen all the damn time. Sure we don't like our focus interrupted, but that's what work is. It's dealing with the managers and leads that need to ask you something urgent while managing your deadlines and dealing with noise which is still very much present in a closed-office area unless you are the board members that get to work remote.
I have one cool little experience which was an open office that switched to a closed office space during my stay. Productivity went down regardless of the boundaries put in place because now the leads and managers have their offices closed for meetings and therefore engineering staff is next in line to handle emergencies/data requests. Granted this is due to our workflow as well, however the point I'm making isn't that one setup is always better than the other but that it probably depends on multiple things and if you think you're gonna get 4 hours of golden time in a real, moving business then that's very naive or you have been very lucky yourself.
I think the reason I liked open offices is because when I needed to rethink an algorithm and analyze it I had at least 3 people that could offer their commentary. And while study groups may not work for reading a book, they damn sure work on designing algorithms when you need to openly discuss the tradeoffs and goals. Just my 0.02 on the whole thing but TL;DR sounds like open offices don't work for some places, but work great for others.
EDIT:
to add to this, the open office we had was not noisey. There weren't massive conversations happening all the time and it was normally just inside voice levels of noise. I haven't experienced what I am imagining as the restaurant equivalent of an office.