Just do it for your self: Count Together all the weight you want to carry. and than try it out. I dont say its kind of that soldiers cant carry more i mean just for you so you know about what kind of weight we are talking. BTW the Weight cap for force walk is 45Kg.

Ok, i should edit this.

Turns out, it's BACKPACKS that are the real villain.
Wut? Backpacks are light, it's the stuff inside that weighs.

Since downgrading the size of the backpack fixed all my premade classes, one or two i had to remove a mag and a grenade.
But backpacks, Wheeew, those are heavy. (Apparently)

Knocking your head on the wall of realism is not a solution. OK, in real life I'm unable to run with my after-school snack. Not too serious cause I don't go to school any more!
As for every disappointing gameplays, cheaters and even adult scripters find solutions to bypass these points. It takes few time to have your own addon and no more problem with fatigue/stamina, even if some servers kick you (not so much).

The problem is: how BI can satisfy most of players, avoiding such bastard solutions?
What about home made (but great mods) with plenty of magical equipments (extra-huge backpacks, light weight machine guns with Uranium bullets, light but super-efficient armored vests...?

The answers are:
1 - a charter for "compatible" or "BI consistent" addons which complies to the vanilla statements (equivalence in weight, armor, capacity, velocity, power)..
Scripters should declare to be compliant with this charter (something like signature for addons);

2 - Difficulty settings, BI in charge of that point...