In my matches, Olaf is a bigger threat than Annie.
A lot of the $4 champs tend to be carrys. They're available much sooner than the $5, so it's easier to stack them properly. And they're ALMOST as good as $5 champions. (There's only 10 of each $5 champion in the game. Well, there's only 12 of each $4 champion. The T4s are closer to the T5s than they are to the T3s.)
Ashe, Kha'Zix, Twitch, Yorick - All very strong and contested champions. Brand has some of the highest DPS in the game. (But Brand is more sensitive to item build than Annie.)
Annie is interesting because she has only two traits, yet desired for builds that include neither trait, fitted as a Mage. This successful strategy may have been unintended.