I like how you guessed the exact weight of a video game armor just by briefly looking at it.
Even medieval full steel plate mail only weighed around 35kg / 77lbs tops and knights could run, fence, roll and make back flips in it. With todays composites and light ballistic fabrics armor weighs far less so I find it endlessly amusing you assuming the armor in a video game taking place far in the future weighs 150 kilograms and encumbers the wearer. Armor in the 14th century didn't encumber the wearer much, I guess 800 years later armor has become even better. 
But if you want to find excuses to run around on the battlefield -where the air is filled with razor sharp shrapnel and bullets traveling several times the speed of sound- in ''revealing armor'' or even as you mentioned, with a naked upper body, be my guest.
You might be a little bit quicker but can you outrun and dodge shrapnel and bullets?
Back in the 80s when I was a kid, my favorite toy was GI Joe. And among them, the ones I liked best were those who wore heavy armor, they were theoretically strongest. Until one day my father explained to me that a helmet was not designed to stop a bullet. It simply does not have resistance to do it.
Then I began to see armor with different eyes. I can not look at a bulky armor and find idiot. That´s the best post on this thread (only read pag1 and 33 lol)
Here's the thing: bullets aren't the only thing people need to be protected from in a hostile environment. The lore says that shields are designed to stop projectiles moving at a super-fast velocity while ignoring slower-moving objects. That's why people are able to, for example, sit down in a chair with their shields up.
But our explorers also need to be protected from other hazards - like falling debris, shrapnel, extreme weather conditions, animal bites, melee attacks - and that usually involves some additional blow-absorptive padding. They need enough room in their suits to accommodate their health monitors, oxygen supplies, pressure stabilizers, medigel dispensers, battery packs, and maybe even to carry some additional survival gear.
You want to protect yourself from bullets? Kinetic barriers.
Want to protect yourself from environmental dangers, splinters, etc.? Armor. LIGHT ARMOR, because you also may need...I dont know, climb a ladder. Or crawl through a confined space. Or get up if you fall.
Talking about other games as a example

some really heavy armors here (love the guy with a skull on his visor). But the Spartans have superpowers, they are much more strong then a regular man. Noble Team are awesome.
Now, look at this MESS

Had a very interesting topic in Bethesda´s forum where a real-life military made heavy criticism of this armor. The main point is that no one in their right mind would use that kind of crap in the legs. I doubt you can flex it.
And that type of armor is very Mass Effect look like (I speak of the fact that every part of the body has a metal plate).
He said the best and most realistic armor from the serie is the Veteran NCR Ranger. A helmet, a coat, a gas mask, boots, jeans, and a bulletproof vest.
Back to ME, what's with those shoulder pads? Why? WHY? What is the purpose of that extra weight?
Now, all my criticism I do in relation to weight and mobility and I see that you put the issue of the weight in check. But understand, the visual impact bother me. I look at this armor that I posted before and I can only see someone falling and trying to get up and failing, like an upside down turtle.
So that´s why I go to the battlefield with a naked upper body 