actually they made some point here. nostr is not a first mover in social network so it has no such advantage, I agree, but the real meaning of that point is to say social network is not the killer app on Nostr. Instead, I believe we have more interesting stuff to build on.
Discussion
First mover advantage is not everything. MySpace had first mover advantage. So did Netscape. And god knows how many other companies.
Timing matters and so does positioning.
In fact, in the startup world it is well known that the 2nd batch of players can do better than the first.