Casual WHM-7S "Nonstop Zap and Woosh" (3xLRM10, 3xLL, XL325) + alt (TAG, XL300)

EDIT: 2nd iteration drops a TAG in favor of another DHS

Spoiler: Previous iteration with TAG

3xLL (comparable to 6xERML but with better range and lower cooldown) combined with 3xLRM10 for indirect fire support (so you can shoot at anything even without Line of Sight) combined with excessive cooling and a bit oversized engine.

Stick with the main group and poke whenever you are cool: if you fire your LRMs only you will be heat stable (you will actually cool down with maximum cool run and heat gen), so poke with LL and add LRM either when there is no line of sight but a lock is available or whenever you are running cool. With 3xLL only you will achieve a 60% cooling efficiency and ~6 alpha coefficiency, which means you should be able to hold your ground with LL only to pinpoint damage to the chosen target.
Also, LL have an optimal range of 450 meters (~500+ meters with full range skills), which is also the recommended / optimal range for LRMs lock and travel time, so there is a nice synergy between them. As stated earlier, stick with your team and fire your weapons accordingly to the situation: LL for direct LoS (add LRMs if heat is low), LRM when there is no LoS.

As recommended skills I suggest to get most of firepower as well as operations and sensors for best damage application and further enhance this "half tank, half artillery" build.
About consumables, I suggest coolshot and airstrike (replace airstrike with UAV if you prefer to shoot back to anybody chasing you, but even an unskilled airstrike could potentially kill a 20 tonner when placed correctly and said 20 tonner isn't fresh).
https://kitlaan.gitlab.io/mwoskill/...0000000000000002871667ee5dff7000000#s=Weapons

ALT: XL300 version with a full 4 ton of LRM ammo and maximum armor to soak damage with those nice arms.

 

EDIT: dropped TAG in favor of another DHS
3xLL + 3xLRM10 is a better combination due to better cooling and more zap and woosh. TAG precision bonus is negligible and you'd better off picking target with 3xLL anyway. I think I've found a build that I finally like on this variant.

 

I'm not sure about it: last time I've checked Excalibaard utility guide TAG should provide a bonus to spread, which should stack with direct LoS and artemis.