I'd love to see the ATMS get a slight buff, they really seem a bit flimsy for the effort involved with them.
I also agree more variants wielding them would be fantastic.
I think that the main problem with them is that they seem to be carried by inferior variants, particularly energy sniper/missile boat hybrids. I think they'd be pretty strong on missile boats. A Vulture with 4xATM12 would probably be a monster of a mech.
Let's see what carries ATMs:
Morrigu C - bad synergy with its CERPPCs, I feel like they've been put in only to fill the pods. If I was driving it, I'd try to snipe from 900 range with my radar on passive if possible. Closing into ATM range and using active radar, just to fire those two ATM3s, doesn't seem worthwhile.
Cougar E - with those weapons I'd like to stand 500-600m away from the brawling and do a fair bit of damage. However, because of its lack of ECM and the necessity of keeping active radar on, it's basically inviting enemy brawlers to come and kill it. With a minimum range of 150m on the ATMs and with Cougar being the slowest light mech and the least armored one in its speed class, it has no chance, especially since in the early game the enemy is likely to be piloting fast assets.
Hep C - I never tried tagging seriously, but if I did, I probably wouldn't want to reveal my position by shooting ATMs, or give the enemy the incoming missile warning. On the other hand, if the goal was to support the team with electronics and keep them under AECM, I'd definitely take Hep Prime over this.
Sulla E - I don't fly but I don't think I've ever been attacked by one.
Blood Asp B and D - ATMs are only there to fill the nose pod. I'd replace them with direct fire weapons or extra heatsinks if given the opportunity.
Steel Rain Huit - ATMs are useful for overwhelming enemy LAMS, but in a Huit you don't want to be any closer to the enemy than absolutely necessary, since it can't run away. The potential problem is compounded since the ATMs are less useful as point defense weapons than the LBX10 or ERMBL. Also, for the anti LAMS purpose, LRMs have superior range, number of missiles and AFAIK a lower price.
Loki D - I think that (S)SRMs would synergize much better with its MHLs.
Madcat E - Again the CERPPC and ATM combo, this time slanted more strongly towards missiles and not carrying GECM. Sniping and missile boating are different tactics, for the same money this variant costs you could get a mech that specializes in either of those.
Thor B - I just don't understand Thors.
Vulture D - Another sniper/missile combo.
Siege Engine MKII - wow, a mech with ATMs that I like. No complaints on this one, the damage over time the UACs synergizes well with the ATMs.
So, what I'd like to see are ATM boats, and more variants that carry damage over time (not burst damage) style weapons.