I'm not really sure what to make of this build but the dakka is a lot of fun and the HM's agility and arm mount weapons seem to scare the crap out of lights. https://mech.nav-alpha.com/#2016f67a_HGN-HM If anyone has any improvements, please, have at it.
There is probably too much RAC ammo and from my experience Medium Pulse Lasers on assaults are wasted: you are very slow and huge to benefit from them, so that's why IMHO they are mostly a light's / medium's weapons. Last but not least, RACs do not benefit of cooldown quirks, RAC2 and RAC5 have different "burst" duration (RAC2 jam bar fill up slower compared to RAC5) plus you have 3 different projectile speed to worry about (RAC2, RAC5 and especially MRMs have different speeds). If you want to fully exploit cooldown quirks, this is the most pinpoint build I can think of... 2xAC5, 2xPPC, LE325 https://mech.nav-alpha.com/#84bb7292_HGN-HM If you prefer something similar to your original build, the following build is the closest I can think of. 2xRAC2, 3xLL, 2xRL10, LE325 https://mech.nav-alpha.com/#cad98815_HGN-HM Probably a bit too hot and not even close to be optimal, but with most of its weapons on arms, it should be quite fun from mid to short range (and 2xRL10 panic button should prove usefull to either tear open a mech or add some crits)