The incentive may help encourage nodes to stay honest. If a greedy attacker is able to assemble more CPU power than all the honest nodes, he would have to choose between using it to defraud people by stealing back his payments, or using it to generate new coins. He ought to find it more profitable to play by the rules, such rules that favour him with more new coins than everyone else combined, than to undermine the system and the validity of his own wealth.
That's the game theory.
That WAS the game theory BEFORE the cartelization of mining. Satoshi did not fully know future. How could the community express themselves if their ability to run a full node was taken away?
Nope. That is Plan B: What if "a greedy attacker is able to assemble more CPU power than all the honest nodes"?
"The community" would come here, start a topic and warn about the shit, it gets viral and the attacker and his coins are doomed in a few hours. Full nodes aren't helpful in most attack scenarios anyway.
But full nodes do secure the network. Any block/transaction that isn't following the consensus rules, won't be relayed. Bitcoins is actually a network of validation.
Relaying blocks is not a big deal. Your argument is not qualified enough to be discussed here, sorry, blocks get relayed anyway, e.g by collided pools. Plus, full nodes are not able to detect mal-incentivized reorgs and censorship the most practical threats due to mining centralization.