If Netflix were working correctly and could handle the load, you'd absolutely be correct.

But it does seem the capacity of a hybrid system of Netflix servers plus P2P would be strictly greater than either alone? It's not an XOR.

And note that in this case of "live" streaming, it still has a few seconds of buffer, which gives a bandwidth-delay product of a few MB. That's plenty to have non-stale blocks and do torrent-style sharing.