I don't know how this game works, but in TT, good lights are flankers. The ones that are so poorly designed as to be incapable of that are described as "scouts" because they're too useless to do anything other than look at the enemy. A Jenner, Javelin, Locust, or Commando have the tools to do a lot more than just look, however. (Does the game have FS9-M Firestarters? Those are premier backstabbers, and a real prize to have in your bays.)
A Locust that dashes up behind a 'mech gets a +4 to hit, so everyone's shooting at it on 8s
at best which is a ~40% chance to hit. A couple of medium laser strikes isn't going to kill a Locust either, so if you want to level it in one shot, you've got to hit it with something big.
Firing arcs further complicate matters, if none of the target's lancemates are able to look at you, then anyone shooting back is only shooting back with one arm. Which prevents them from bringing insta-gib levels of firepower to bear... and they're still missing 60% of the time (or more.) Ultimately, they're probably not even going to bother, because some of your less mobile 'mechs are providing more desirable targets.
Of course, if they're taking evasive action too, then your return fire isn't going to be terribly accurate, but it's striking weak rear armor. A lot of 'mechs have really lackluster rear armor -- a single medium laser can melt through the armor of a Hunchback side torso and score a nasty crit for example.
Also important, light 'mechs can usually position themselves to get a kick without letting the target get one too. Again, a lot of 'mechs don't have strong legs -- a Warhammer's got 15 and a Marauder 17, and it doesn't last long.
I'm not sure how good they are in this game, I don't think the game has kicking??? which would make light 'mechs a lot crappier. Also ammo crits aren't instant kabooms anymore, which is a
mixed blessing but probably also puts lights at a disadvantage.