This is what I envision a Commander's version of the Atlas to be. It has a decent punch at all ranges. If the Gauss rifle wasn't so easy to destroy in MWO, I'd probably replace the AC/20 with a Gauss rifle.
A single LRM15 rack is unfortunately not going to do much against AMS, one enemy with one AMS reduces that by 7 missiles. If there are two with AMS it's only a single missile that maybe gets through. Your alpha below 180 range is 38, that's in the heavy scale. Assaults should be 40-60 dmg given the current meta with high alpha strikes, so unfortunately this has low survival odds vs a maxed weight. Sorry to come across as negative, I do like the thought and have a similar build myself.
Thanks for your feedback. But I'm not into the whole "min-maxing" thing. I play for fun, and I love to design 'Mechs. This 'Mech has served me well and the LRM-15 seems to do well in the games I have played.