If that Hunchback has more speed than a normal one it could win because all he needs to do is to get something between them and create some distance.
Once he has done that he can easily stay out of the effective range of those LRM's while legging the Atlas with the AC2's to make things even more easy.
Even if he the Atlas manages to launch the LRM's at maximum range his accuracy will suffer because of it.
Especially if the Hunchback moves fast sideways before the LRM's impact. All you need to do to confirm this is watch the Heavy video with the Catapult when he opens fire on a fast moving Jenner.
Most of those LRM's misses the Jenner in the video because of distance and speed.
AC2's may be weak but an they easily outclasses an LRM 15 rack when the Atlas can't get close enough to take advantage of it's superior firepower.
But if the Hunchie doesn't have a big engine it's all over. Now i solved the problem. Where is my price? Give me my beta key please.