[Metalsheep]

I like the idea of a "mech" being more of an Exo Suit rather than something like a BFR. Like an outdoor, Heavy MAX as has been said already. It could have about the same armor as a Lightning, maybe a little less with no shielding at all. And equip an AI/AV weapon, since the Lightning covers the AA aspect of the lighter vehicles. Like a machine gun and a shoulder mounted rocket launcher. Slower moving, but might be able to get places standard vehicles cannot.

The MBTs should be able to handle them easily 1v1. I would think the ExoSuit could be more like a Fire Support vehicle, it sticks with groups of infantry and lends its extra muscle. Great against softies and other light vehicles, weak against Aircraft, larger groups of softies, MBTs and other heavy vehicles.

Kind of like those AMP suits from Avatar, they're larger than MAX suits, but not as huge and powerful as the BFRs were.

I could also see how they could have utility outside of combat, such as a Heavy Lift vehicle for large engineering deployables or other heavy work. (Not that this should be included, but it makes a reason for them to exist in Lore for both combat and support work.)