I agree with your assessment of Dragon Dynasty. DD have done a great job thus far in releasing Asian films for the U.S. market (e.g. Hard Boiled). It's a shame because Supercop is one of my favorite Jackie Chan movies. It's quite insulting to change the music soundtrack in such a way. The people making that decision don't seem to have too much respect for other cultures. I suppose the reissue team thought that the original score was "too Asian" and by replacing it with hip-hop, would make the movie more appealing to people in the West.
I was lucky enough to actually view the uncut Hong Kong version at a local theater in the early 90's. I hope that other Hong Kong films worthy of being reissued (i.e. The Killer, Drunken Master II) will not contain any detrimental editing / cutting. Perhaps a future Blu-Ray version will contain a full presentation of this great film. Until then, one might have to get a region-free DVD player and buy one of the international versions of "Supercop."