It seems to me that this is the intention.

It certainly used to be when they would actually call row numbers and now I guess it's similar, but refined with the Zone system.

Big ^ to NMs answer, but given that reality, I think the real problem is with enforcement.

I actually tend to try to be the last to board, so I haven't paid close attention, but I don't recall often seeing any GAs actually checking to see if the right pax are boarding or more importantly sending away those that are trying to jump ahead.