People makes some confusion because MS marketing.
BC Pack uses loosy algorithms... there are loss of quality in the final result (the texture will lose quality).
Kraken uses lossless algorithms... there no loss of quality in the final result (the texture quality will be the same)
Kraken should be compared with Zlib on Series X.
BC Pack probably with Oodle on PS5 (that is a guess).
The 4.8GB/s avg. on Series X is using BCPack that have a better compression ration because it discard data making the data less accurate.
The 9GB/s avg. on PS5 is using Kraken that will maintain the exactly original quality from beguiling to end... so it has lower compression ratio.
If you guys wants to understand better it is the same case for MP3 vs FLAC.
MP3 is a lossy format, which means parts of the music are shaved off to reduce the file size to a more compact level. It is supposed to use "psychoacoustics" to delete overlapping sounds, but it isn't always successful. Typically, cymbals, reverb and guitars are the sounds most affected by MP3 compression and can sound really distorted or "crunchy" when too much compression is applied.
Like MP3 before it, FLAC has been embraced by the music industry as a cost-effective way to distribute CD-or-better-quality music, and it doesn't have the auditory problems of MP3s. FLAC is lossless and more like a ZIP file -- it comes out sounding the same when it is unzipped. Previously the only way to get "lossless" files was via the uncompressed CD formats CDA or WAV, but neither is as space-efficient as FLAC.
The comparison was always dumb to me because Kraken and BCPack have different purposes.
BCPack can be used only in assets that can lose quality (mainly textures).
Kraken can be used to everything.
You won't use BCPack for a game binary for example because after the decompression the binary won't work because it lose part of it data but you can compress a game binary with Kraken.
That is a dumb example because game binaries is not that big to need compression but it gives you the ideia.