If a light mech player is very experienced and an assualt mech player is also expereicned, then what would happen is that the two would never damage each other, never meet each other in battle, or will kill each other at the same time.
Why?
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If both piolots are theoretically equally good, then neither would even damage each other because the light piolot will avoid the conflict that he will surly meet face to face as the good assault pilot has put himself in a position where it's very hard and risky to make an encounter without causing serious damage.
That was the matter I was trying to point out: you need a balanced game. The scenario you described will only happen if the game mechanics is not broken. Thus both the assault pilot and the smaller mechs need to use their brains to make it work.
But if the game is broken, like in MW3 multiplayer example I mentioned, then the smaller mech pilot will not avoid conflict because the assault can be taken down by direct engagement.
So if it works in MWLL the way you described, then I am happy, it means we can expect a balanced game, where tactics and skill win the day. Instead of having to exploit a broken game mechanics that is mistaken for "skill".