Desoxyn is legally prescribed meth. Adderall isn't quite the same thing, but Desoxyn definitely is.

Not entirely true. Methamphetamine has two enantiomers, dextro-methamphetamine and levo-methamphetamine. Desoxyn is 100% dextro-methamphetamine, while most street meth will be a racemic mixture containing practically equal amounts of each enantiomer.

Which to be honest if you ask heavy amphetamine users amphetamine and methamphetamine aren't that different anyway.

I would say this isn’t true either. Both impact the CNS is much the same way, but the addition of the methyl group allows for meth to much more easily cross the blood brain barrier, producing markedly more psychological and euphoric effects. Methamphetamine also lasts 2-3 times as long.