Why?

5.7 Hemi is basically roller 318 with a 360 crank, sure its got variable displacement and now variable cam. EFI and OD can be installed on any LA/magnum so really not much of an advantage. It's really just a head package on a redesigned LA short block. The head flow is where these engines shine needing a lot less cam to build big power numbers. Really unfair to compare the power numbers of an LA/magnum engine compared to the hemi cause the cams run in the former are way under cammed even the 340 cam is barely a performance cam.
If you ran a similar cam that's in the hemi in the magnum you see less of a power advantage even with the less head flow, swap on a set of Eddy's and the advantage would even shrink further same with the weight advantage.