cp is designed to copy data from one file to another. Block devices are represented as files, and cp won't be speed limited by block size. dd is also designed

cp is designed to copy data from one file to another. Block devices are represented as files, and cp won't be speed limited by block size. dd is also designed to copy data from one file to another, in blocks, with optional conversion of the data (eg, from EBCDIC to ASCII), and with optional offsets/limits to copy regions of a file. dd is not designed to copy raw block data, it is merely a different file copy tool.