I thought several countries tried the intermediate rounds (ww2 Japan Ariska for example with the 6.5 , and the Swedes for that matter and found them good for soft targets like flesh that they didn’t have knockdown or penetration power on objects) and didn’t like them?
I will admit, penetration and knockdown being inadequate is something I know little of. My understanding is that it was more volume of fire, and ability to engage out to 300 meters is what Germany was going for when originally fielded the Sturmgewehr and 7.92 Kurz cartidge. I know a little more on the how and why we ultimately chose 5.56 mm. I might recommend looking into Chris Bartocchi on this one, he has a YouTube channel that’s also the same name as his company Small Arms Solutions. He’s has a wealth of knowledge on these things, particularly the development of the M-16 and M-4.
Oh, and that was the idea with the intermediate cartridges, volume of fire, manageable recoil, and a modest range for engaging point targets.