You, Sir, are a moron.* I would suggest doing even a tiny bit of reading before you make such emphatic statements. If you're going to tell everyone that something commonly accepted as fact is actually false, you would be well advised to double check your work. Re-read that article. I have the full copy, but you can find everything you need in the abstract.
It says that lisdexamfetamine is metabolized to dexamp by an aminopeptidase in the red blood cell cytosol. Did you bother to look up the word peptidase? Since it has the -ase suffix, you know it is a type of enzyme, and the peptid part... hmm, sounds like peptide... Oh yes, peptidase, enzymes which cleave peptide bonds. You should look up examples of that type of enzyme. I'll wait a second while you do so.
Done now? Okay, good. Now don't you feel stupid, or what? Yeah, trypsin is a common peptidase. It is perfectly capable of cleaving that bond in the lisdexamfetamine molecule to release plain dexamphetamine.
Moreover, that study doesn't say that LDA isn't metabolized to DA in the gut, it just shows that LDX is metabolized at least to some extent by red blood cells. It looks specifically at how red blood cells metabolize LDA in vitro, it doesn't address how the drug is actually metabolized in vivo. The idea that red blood cells actually do the conversion would suggest that injecting the drug would make it work significantly faster- bypassing long route it had to go through the stomach, small intestine, active transport by amino acid transporters, and more before finally hitting the blood. That may be true, actually, I'm not completely sure, one small study found peak plasma concentrations of dexamphetamine to occur at 2.58hr after IV admin, while much larger studies find about 3 to 3.5hr for oral admin (with wide variability). Because of the wide individual variance, I don't know how much effect you can read into the seemingly faster time to peak plasma from such a small sample size. Too much noise going on to ascribe the difference to any one cause.
*I wanted to say idiot, but that suggests you're incapable of intelligence, and I don't think that's the case. I think of a moron as one who is capable of beneficial change.