classical arrangements of popular music are always shit IMHO.
The former is based on harmonic and melodic complexity expressed through several dozen instruments - whereas - say - guitar based rock is based on far more simple structures where the complexity and nuances is in the dynamics and texture between the drums plus two or three instruments. Something like Jonny Marrs guitar does the work of an entire string section in an orchestra.
Then you have the focus on the charterer and personality put across by often quite idiosyncratic voices. Classical singing is far more about using the voice primarily as an instrument - rather then a direct expression of an individuals personality.
It always seem to end up with something bland and banal that does a major disservice to both traditions. Many many rock musicians have gone down this path - presumably in search of some sort of higher artistic validation - but it always ends up making their music sound infantile.