The first melee mechs to clash against each other weren't the mechs charging at each other in the center. Space knights and other sturdy mechs took up the vanguard. Their heavy shields and their resilient frames allowed them to resist a lot of damage, making them ideal to lead the charge.
However, the need to stay behind their limited protective envelope meant that a lot of faster mechs had to limit their speed and acceleration. A unit of mechs only moved as fast as its slowest machine, and space knights that piled up lots of armor weren't known for their mobility!
Fortunately, it was not that big of a problem for them to accelerate straight forward. Many space knights incorporated specialized flight systems that were hardy and not that easy to damage. While they did not have the power to induce a lot of directional forces on the mech, they compensated for that by putting most of their efforts into moving forward.
