Original 10mm vs .45acp
How was 10mm better?
Faster, flatter trajectory. More power. Better penetration.
In its original configuration, 10mm had the same energy at 75 yards as .45acp did at the muzzle.
Also, due to its slightly slimmer profile, more rounds could be carried. Note the Glock 21 with 13 rounds, and the Glock 20 with 15. Not much of a difference, but still an advantage to the 10mm.
If used in a pistol/carbine pair, the 10mm seriously outperforms the .45 from the carbine.
The round just never quite caught on. The average buyer doesn't like .41 magnum type recoil. The average Fed didn't like it, either.
That said, I own 3 .45's, and no 10mm's.