this is just my opinion. as long as there are living beings in the galaxy, no one "wins." just temporarily puts a stop to things. there will always be psychopathic lunatics like there will always be people looking out for the best interest of the galaxy.
Sure the lunatic might get killed, but there are plenty of others beings to replace him. same goes for the good guy.
He has a point. For a time Luke Skywalker was the last jedi in the galaxy. Fighting two siths, one his father, the other was proclaimed the most powerful sith lord of all time, with a whole empire behind them, using nothing but a small rebel force, a small rebel fleet, and some ewoks, he won. Later made a new jedi order. Pretty good considering the odds.