When the Orb explodes at the end, it sends out 18 shards. If a monster stands right at the point of impact, he will be hit by every single one of them, making it an extremely effective way to kill bosses.
A very average 400 Frozen Orb damage will net a very nice 7200 damage if all 18 shards hit, not counting all the subsequent shards randomly launched by the orb.
And the fact that Frozen Orb does not gain any more synergies is what makes it so versatile. You can use it with another skill tree without sacrificing killing power.
If you can't learn to do something well, learn to enjoy doing it poorly.