If the debugging of the network protocol can be done by subscribing to packets and analyzing them, you might be right, but that basically requires that the network stack is actually functioning. If something is broken in that infrastructure, then it becomes hard. Why is the thing suddenly stalled? Where is the leak? Where is the memory corruption coming from? At that point it’s not about looking at packet data anymore, but at looking at all involved (thread)state. And that is incredibly hard with GNRC.