Which suggests that the US's longer sentences and higher incarceration rate are unnecessary for reducing recidivism, which is often what's argued as justification (keep those people off the streets, etc).

It suggests that the OP was misinformed and deductions from false data should be considered carefully. Might still be. Might also be total nonsense. It's a claim that rests on no data.

I think generally you can't compare the US with European countries on many things. The US are much more individualist, wealth is much less equally distributed, the population is much more diverse, there's still a lot of the frontier mindset. That'll create a different profile which you can see in e.g. entrepreneurship, and probably also in crime-rate.