No it's not, the author "failed" to mention that the vast majority of networks drop spoofed packets. It may be exploitable inside a target network, locally, but one usually has a lot better options if he has a foothold there, than bruteforcing sequence numbers with gigabytes of traffic for a single connection.
Steady on there. The author has clearly done a lot of work on this and while your points are valid, that this method of attack isn't new nor practical, he has still learned a very genuine potential vector for attack. Thus it deserves a mature discussion since there will certainly be others who might learn from the author's research.
I'm all for constructive criticisms, but calling his article "dumb" is just unnecessary language. It doesn't contribute anything and yet could discourage authors from publishing future work.
Anti-spoof measures are really only effective close to the edge, further in packets are routed with abandon because of overhead and difficulty in verifying the origin.
Counting on the attacker's own network to have egress filtering stopping his attacks, isn't that a bit like discounting spam because most networks filter outbound SMTP?
If your defenses are predicated on the assumption that you aren't going to encounter bad stuff due to filtering at the source, you are in for a bad time.
It's dumb is what it is.