Concepts like 3 to 1 ratios are only valid when comparing like or similar capabiity systems, weapons or units.

comparing the average WW2 infantry platoon armed with bolt-action rifles and a limited number of MGs to any of today's cutting edge infantry with magazine fed assault rifles, ICOM intra-squad comms, body armor etc will reveal that a straight comparison of numbers only is invalid. The concept of Relative Combat Power was an attempt by the US during the late 80s early 90s to address this issue. Sometimes it worked, sometimes it did not.