Light body type dies easier and for the life of me, I can't find anywhere on any map that a light can go that the medium can go as well. Other than a bit more speed, I don't see the benefit....

You haven't found the extra ways to use the free running yet, and you haven't been using its incredible flanking abilities. Jump from a high ledge into a slide for extra speed to rush the enemy with your smg then spray them in the face then run by. Also, sniper rifles are light weapons, so use them with hit-and-run tactics. Light is a very skillful weight to use.

Hell to the yes they are.

Protip: Learn where you can walljump, and slide EVERYWHERE. Don't stop sliding around, every time you hit the ground, every time you round a corner, whenever enemies are shooting at you, keep sliding.

I always use the Light body type. For me, I'm either fine, or someone gets me in their sights and I'm screwed, so the health isn't an issue. Also, if you can't find places to use their advanced SMART abilities, you aren't looking hard enough. From getting around things really fast, to getting to places a much shorter way they have a HUGE advantage. There aren't really any places that ONLY lights can go, but I think this was a fair balancing design option. It would be lame if Lights could get up in some stupid place to camp or something. They can just do this much more effeciently and like 100x faster and more easily.

Light is made for objective attacking. If you're trying to shoot and kill like the Scout in TF2, you're doing it wrong.

Objectives and Teammate buffs ONLY. If you're shooting, NEVER stand still, and never walk for more than 5 seconds. SMART is mandatory for Light.

But im watching the lights on my team to get an idea because i haven't really found anything and they don't seem to be doing anything really spectacular.

All the body types have there pros and there cons. The light body type however, the cons outweigh the pros. As the only pro the light body type has is the faster moment speed and the ability to get to certain areas the medium and the heavy can not. These areas though are kind of limited and in my experience.

Mediums only have 20 more health. Thats like 1 bullet difference if your being shot by an AR. Your a lot faster as a light, and you can get to places and take routes no one else can. I find the light to be worth it.

If weapons are a problem, I've found the Bulpdaun to be a good SMG for lights. It has better range and stopping power than most other SMG's, although it's lacking in the clip size/reload time department. But that's what a backup weapon is for, amiright?

Hell yeah, love the speed and believe me, there are enough places a medium can't go but a light can wallhop and jump to reach some ledges.
I'm wondering if a medium can get on that lookout post directly above the big wall (= first prim obj) in Container City..?

It's also insanely accurate when you aim down the sights. Thank god for Bullpup designs.

No, really, look at this link.
http://denkirson.xanga.com/738334226/brink/

Bulpdaun gets 0.8 accuracy when ADS. Smaller is better. That's the best accuracy you can have for SMG's.