The way that this shows that Odysseus is a good leader is that it forces him to make a really tough decision. Odysseus knows that he will need to sail very near the Scylla to avoid the Charybdis. He knows that if he does, some of his men will be killed by the monster. But he also knows that if he does not, all of his men will die because they will be sucked into the whirlpool.
So Odysseus has to decide whether to sacrifice some men for the sake of the rest or to try to get away with all of them alive. He knows that he is very unlikely to get them all through this narrow passage alive so he makes the tough decision and lets some of his men die. This is a hard decision and making it shows he is a leader.