If you don't like the terminology (none of which I invented, I must again lament) you need only not read this thread. I don't know why you must nit-pick everything I type.
There is no "breaking point" between what is considered a modern full-power rifle cartridge and an intermediate one. It's more of a gray area. I can give examples of each.
Full Rifle: .308, .30-06, 7.62x54mmR, 8mm Mauser, .45-70, .270, etc.
Intermediate: .223 Remington, 7.62x39mm, 5.45x39mm. Originally thought up by the Germans during the second world war (the 7.92mm Kurtz round) as a midway cartridge, more powerful than 9mm submachine guns but less recoil (and power) than the standard 8mm service round. The first operational intermediate cartridge rifle was the MP44/STG44. The first one to see real wide scale use was the AK-47. The United States didn't get in on the game until the late fifties with the development of the AR-15/M16 family.
Gray area: Things like .243, .30-30, etc. But in military terminology, it's generally one or the other. Most militaries use a full rifle round for machine guns, a few battle rifles, and scoped weapons, as well as an intermediate cartridge for standard rifles and light machine guns. NATO uses .308/.223, whereas Russia has the 7.62x54R/5.45mm combo.
But you probably knew all that.