Some of this is a little more difficult than it first appears. Try on a ballistic vest with a knife-weave through it, say seven or eight kilos, then add an equipment belt with handgun, extra magazines, metal telescoping baton, spray and cuffs and tiny torch and a radio, say another 10kg. Then run a 400 meter obstacle course with the equivalents of suburban 6ft fences, railway platforms to jump up onto to, windows to climb through, 20ft cyclone wire fence, plus a few other delights. The final result, shaken and not stirred, is a puffing sweating person who needs a bit of time to catch their breath. This is far worse than having to just wear it around for nine hours in the course of a regular day at work.
Do things differently with webbing, 180c of 5.56 ammunition, rifle, water, rations, ballistic kit, helmet, etc etc, and doing patrolling before having to engage in fire & movement, and you end up with similarly tuckered-out person.
My overly verbose point is that it's not so much the weight that is carried, but the the combination of weight and activity level that is critical. An unfit person may not be able to do much with that sort of gear on at the best of times, but even the very fit will be tested depending on the level and duration of intense physical work.
I reckon END is at least as important as STR in this consideration.