There are some builds that can ignore completely energy, rendering them immune to energy weapons, which is not fair. For example full heat builds or machine guns. It's strange how a mech could go on with 0 energy, there should be loss of movement if energy is 0 or every weapon should consume energy, even if very little.

I disagree. The Mechs do not run on energy [what exactly do they run on... things that make you go Hmm.], the weapons do however. Those of us who choose to fight using energy builds realize this and that is part of the technique of it all. Having no or even low energy may not eliminate all the weapons, but it does eliminate specials as well as drones. The elimination of the Drone is a very serious matter. On top of that it also eliminates one of the most destructive class of weapons... the Swords.

You most also remember that to compensate for all there uniqueness, heat builds and there weapons are also the weakest in terms of dealing physical damage, especially damage over time.

As for Machine guns, most are close range and you have to learn to avoid them.

No build is "immune" to energy.

And last but not least, remember that energy builds and hybrid energy builds are the hardest builds to master, but also the toughest to beat in the right hands. [at least that holds true in my opinion]

Use a physical build then it`s the best kind (in my opinion)