Go-Back-N Protocol not efficient?

Let’s say we have five packets

p1 p2 p3 p4 p5

to be sent sequentially:

and for some reasons, p3 got delayed so it the the last packet to arrive recevier.

so below is the receiving order on the receiver’s end

p1 p2 p4 p5 p3

and according to the Go-Back-N Protocol, the receiver will only send acknowledge of p2 when it receive p5.

then the receiver receives p3 right after p5, and then it sends acknowledge of p3 to the sender.

But there will still be a timeout and the sender still has to re-send p4 and p5,even though the receiver did receive all packets, isn’t this Go-Back-N Protocol really inefficient?