The left forearm is BROKEN! It looks.... every bad adjective I can think of. I was told it was broken for gameplay reasons(VLOG 14) because of how much large LRMs would increase the silhouette. Now, onto how to fix it. Instead of moving the left forearm in closer to the hip, change the shape of the missile box when equipped with an LRM15(3 rows of 5) or LRM20(same with another 5 below or 3 rows of 7 and 1 row of 6). This way the silhouette does not get significantly bigger and the arm doesn't look broken.
Here is how it currently looks vs my suggestion:
(Orange line added for silhouette reference)

I also miss the half-box "shield" that the old 5J and 7K models used to have. It would be nice to have it back instead of the empty box whenever no LRMs are equipped in the arm. It would also be a good place to have custom MC geometry if that ever comes to fruition.
Quick mock-up:

Yes, the silhouette is slightly bigger on my versions but not enough to justify the current goofy arm placement and, seriously, no one pilots a Trebuchet against Tier 1 sharpshooters anyway.