Yes the calibres with the minimum amount of recoil are easier to shoot. One of the criticisms labeled against the 30-06 was its recoil.

Certainly the bigger the hole the quicker the blood comes out. Bullets with better designs for maiming/killing will do a better job then designs of old.

The 6.5 Japs shootability may not have helped claim that many more lives as its effectiveness would rely on good shot placement. Not something that was noted in rushed combat and they where not firing the 123grain spitzer. They were more typically 139 grains.

I do take what the good Lt Col said as personal opinion and not much more, simply as he is the only person I have heard of that rated the 6.5 Jap. Most did not. If they had of used a 123 grain spitzer at a higher muzzle velocity it may well have proved more effective, bit like the Brits dropping from a 212grain bullet in the 303 to a 174 grain.

Most of my reading has shown the Japs going up in calibre to achieve better battle field results against the enemy troops and to standardize ammo in their machineguns. The standard 6.5 rifle ammo proved to hot for their machine guns so the ammo for the MG's were down loaded.