Why not issue both a full power rifle and an assault rifle? Everyone seems to be in absolute agreement that you have to select one single caliber to issue to the entire squad.

WWII infantry used a combination of automatic rifles/machine guns, full power rifles and submachine guns. This provided a combination of accurate long range fire, full automatic suppressing fire, and close quarters automatic fire.

These weapons used at least two different types of ammunition and somehow the supply system held up. Why not consider it again?

The full power rifle has to be as powerful as possible without being overly heavy. The assault rifle has to be controllable when fired fully automatic. It's impossible to do both.

To me the answer to this dilemma is just to use two weapons. For example you could issue full power rifles to most of the squad and reserve fully automatic assault rifles for the squad and team leaders. The weaker round of the assault rifle requires better marksmanship and the fully automatic feature requires more discipline - qualities you expect in your more experienced soldiers. The squad loses three full power rifles, but it gains a significant advantage if the enemy gets close.

You could also issue a full power rifle to your squad's designated marksman. That gives a measure of range and power but doesn't come with quite the same cost in weight. It also overcomes failures in marksmanship (whatever the cause) by hand selecting the squad's best shot.

Having the two weapons already in inventory also simplifies the transition if the environment contraindicates one or the other. E.g. in the desert you would just withdraw the short range assault rifles while in a jungle or urban area you'd likely move away from bulky battle rifles.

I know that the logistical and training issues are supposed to be too complicated. However, all the major combatants in the second world war overcame these obstacles! They covered many different training regiments, philosophies and every type of environment you can imagine. Why is it that we have an absolute commitment to the one proposition that supplies such a ready counterexample?