He doesn't need to come up with a better lineup. An inferior lineup with a higher payout could lead to a fighter expected value. For example, if he has a lineup that wins 1/5 the times the best lineup does but pays out 10 times as much he would double his returns.

It matters to some degree which players he picks, but in the case of GPPs it matters much more that the lineup is unique. There are lots of lineups that have nearly the same expectation.