But even your source says:

or for his life

The argument this is making is that if you sentence a person for 20-40 years, then they’ll be entirely unable to reintegrate back into society once they finish their term; so there’s no point giving someone with an armed robbery charge 25 years, as you inevitably do more social harm then good.

So we’re still back at square one as even your source states that you might as well imprison someone for life.

Also, the source isn’t arguing for or against the death penalty, and they explicitly state that they don’t want to make a stance on it. Instead, they’re saying that a judge should either sentence for 10 years or under, or simply execute a person as there is no societal difference between 25 years in prison or death.