As for World War 2 rations, considering the time, technology and conditions the ration supplied to troops in the field were on the whole good and better than our allies and enemies.
That was not the opinion of those who examined it at the time. It was meant to be an emergency ration for a maximum of 10 days. When reviewed later in the war it was recommended that it not be used for more than 5 unless it was supplemented with other food to increase caloric and vitamin uptake. Most other armies issued camp stoves that allowed less preserved rations to be eaten while away from larger unit kitchens.
Having looked into it apparently the early versions of the ration did include pemmican bars. Though I think they were replaced in the final ration. The main issue seems to be, as identified by
@marathag that the caloric intake was too low and the selection too limited.
In 1942 a paratrooper platoon tested the K-rations in Panama for Jungle effectiveness. However, they only tested it for 3 days and did not patrol in the jungle but rather on flat or gently rolling terrain and cleared roads and only 11 miles per day. At the end of it they were weighed and since there was no abnormal weight loss K-rations were certified for jungle troops. On the strength of this test the mountain and jungle rations (both of which had around 4000 calories per man per day) were discontinued in 1943. If they had done proper testing they may have found some of the deficiencies in the standard rations earlier. This is only likely to affect certain troops, but it was the troops that would be hit hardest by low caloric intake.
Alternatively, you could try shaking up the U.S Army Quartermasters. They apparently hated the non-standard rations as they were more expensive to procure and ship. They continued to insist that one K-ration was sufficient for any soldier, in any environment, in spite of evidence of malnutrition among G.I's in the later war.
The Mountain ration was apparently more efficient in calories provided per pound of ration. If a scaled down version were created for the common ration (3000-3200 calories) it might actually be easier to ship (though probably still more expensive) than the K-ration.