If you're talking about a pair of backup ML, that's fine, but if you're talking the way 3025 designs tend(ed) to overheat, no.
A couple of backup MLs? What is this, a budget militia? MORE FIREPOWER.
By that logic, the Jagermech JM6-DG, Mad Dog C, Annihilator C2, Fafnir FNR-5, and Hellstar all have incredibly insufficient firepower.
Really can't take statements like that seriously in a world where Gauss Rifles, Clan DHS, and Clan ERPPCs exist.
I'll obviously discount any designs that can't actually generate enough heat to be even close to net 0. Then again, ignoring those meant for recon or not having payload for armament, i don't really care for most designs that can't generate enough heat, they're either bad or boring usually.
I don't care for most dual+ Gauss designs at all, they're too boring. Powerful, yes, but often incredibly inefficient, especially if they're Clan designs since ERPPCs are basically better option always. The Mad Dog C is a perfect example, it is quite terrible configuration. Slap a pair of ERPPCs and extra weapons and few heat sinks there and it is far better.
I'll give pass to some like the Tian-zong since it uses stealth and dual-Gauss well while having extra weapons, or the Pillager's Capellan variants which sport stealth armor and extra weapons (the original Star League Gauss model is meh).
Hellstar indeed isn't very good in my opinion, spending far too much weight on heat sinks, if the Hellstar 2 didn't exists, i'd have to pull some to add some ER medium lasers. Hellstar 2 is a massive improvement with its TarComp, it is a 4/6 assault so it can afford a bit of heat to slow down, while the TarComp improves its prowess at range.
JagerMech DG is utter shite, it has way too little armor for its firepower, it will die before it can make good use of that.
The Fafnir gets a pass because it uses dual-HGRs, which have incredible firepower at close range, these are rare enough. But there are many other designs i'd rather use.