Legend Killer "Nailbomb" (1xLBX10, 4xML, 3xMG, AMS, STD250) +Alt

Odd that your 5erll build only has 1 dhs more than this build hahaha.
Ballistic heavy loadouts don't require more than 12 heatsinks usually. The only real heat generating weapons here are 4 mlas. Considering a Jenner with 6 mlas usually carries around 13-14dhs you shouldn't need more than 14dhs for this build.
I just dropped ams like you suggested and upped the engine some. Could drop 1-2 more dhs and up engine even more.

 

MPL:




ML, top speed, armour+:




SPL:

 

None of them look bad. I'm just saying from experience that you could run it with a couple less dhs and still be fine. That std 290 version looks great.

Currently I'm incapable of playing, no access to Internet on my desktop.
But I build and playtest mechs constantly. I've spent twice as long in mechlabs as in game haha. When talking about build heat I've got a decent idea. Purely because I've ran everything under the sun. I've got like 4k matches or something, so lots of hours in testing haha.

Any combination of laser vomit I've pretty much tried. My posts are purely suggestions and opinions either say, so if you prefer your build one way, stick with it. I just post on here for little adjustments to balance people's builds. Just to keep the balance of armor, speed, and heat efficiency. If a build can go faster, I'll make it so but not if it loses too much cooling efficiency. Simple stuff that people normally do anyway, but a fresh set of eyes can go a long way.