The article states a "net-positive energy result", not necessarily a faster time for this specific optimization. They say GZIP decompression is energy-intensive

The article states a "net-positive energy result", not necessarily a faster time for this specific optimization. They say GZIP decompression is energy-intensive, so while the combination of read + decompress may be faster, the CPU load during decompression and memory relocation of the decompressed data ultimately consumes more energy than reading an uncompressed kernel and running it directly.