The quote from Doc didn't include my main point: Most supposedly "new" cartridges provide essentially the same basic ballistics as older cartridges, but in a different case-shape to fit in different actions. Even the 6.8 SPC basically provides .250 Savage ballistics in a round fitting in AR-15's, though with slightly larger-diameter bullets.
Even the .300 Whisper/Blackout isn't very different from many older cartridges, including the 7.62x39 and the 7.9x33, both introduced during WWII. The only meaningful difference in the .300 is the rifling twist, allowing the use of heavier bullets at subsonic velocities. Which is actually more creative than merely changing case-shape so a .300 H&H will fit in a "short" bolt action.
