In Lancer, mechs are rarely slow, stompy behemoths. They are typically agile, adaptable, and frequently able to punch far above their size. They can make use of cover in ways similar to an infantryman, but carry weapons and armor on par with a tank. However, they are not undisputed in their dominance; heavy tanks and VTOL gunships can challenge them, and even foot soldiers can prove a threat in the right circumstances. In Lancer: Alternative, there is also the threat of hostile megafauna to contend with.
Mechs come in many sizes and shapes, from open-framework exoskeletons with jet packs to armor-encrusted artillery pieces on tank treads. Each of the different leagues in the setting has their own style for mech designs, and their preferred equipment to use. But you are destined to be more than a simple grunt, and should not feel particularly confined by those styles and preferences.
Some assorted artwork, for inspiration: