No, the one-armed or head-out-of-water comp swimmer is absolutely NOT more efficient in the water. I can't even believe anyone would make this argument - sheer physics makes this impossible!

Talent is real and I agree it is absolutely the main reason competitive swimmers are well, competitive swimmers. It's genetics. It's not because they were started at age 2 - you take someone with no swim talent ,start them at age 2, and they'll be crushed by the talented one once training gets real. All the non-talents in youth drop out way earlier, who'd continue with that if they couldn't keep up?

But the talent in swim is both technical AND conditioning. These are kids who have awesome VO2, awesome swim muscular endurance, and require a lot less training than an AGer to make big gains. That's why they can swim using ridiculous handicaps and still crush AG triathlete in swimming at 1500 - not because they are magically more efficient (no way) or have better body position (seriously, even with a head out of water completely handicap and against wetsuit AGers?!)

But to get these talented swimmer to where they are, they still had to swim a LOT. Like so much a typical AGer would quit triathlon before they even did the 5-7x/wk practices of a 12-year old girl comp squad for a year, let alone numerous years.

Again, note that I'm not saying at all that comp swimmers don't focus on technique or it's not important to them. On the contrary - I've repeatedly made the point that in comp swimming, technique is likely THE major factor at the high level. At that level, everyone is training to the max, everyone's got great genetics, and everyone's swimming a ton. And when races are decided by fractions of a second, yeah, something miniscule in your technique may mean the difference between 1st and nothing for comp swimmers.