(I also work at RAD on Oodle.)
The Kraken decoders are not "equivalent to 9 Zen 2 cores", that's quoting wildly out of context; by the same rationale a Deflate decoder that hits 5-6 GB/s output would be "equivalent to 12 Zen 2 cores" which is just as misleading. That ratio is just meaningless. They're dedicated fixed-function hardware that does one specific task (that happens to be suitable for HW implementation), certainly not equivalent substitutes for a general-purpose CPU core. If they were, that'd be missing the point.
Both PS5 and Xbox Series X decided to go for HW decompression because they noticed that with a SSD, decompression goes from a side task for one CPU core to a full-time job for several, at which point it makes sense to design dedicated hardware. Once you decide to go there, you have considerable freedom in how you design decompression units, how they are clocked, how many there are, etc., and you configure all that to meet your targets.
In the PS5 case, the goal was for the decompressors to never be the bottleneck in real workloads, so they're dialed in to be fast enough to keep up with the SSD at all times, with a decent safety margin. That's all there is to it.
Along the same lines, 2 helper processors in an IO block that has both a full Flash controller and the decompression/memory mapping/etc. units is not by itself remarkable. Every SSD controller has one. That's what processes the SATA/NVMe commands, does the wear leveling, bad block remapping and so forth. The special part is not that these processors exist, but rather that they run custom firmware that implements a protocol and feature set quite different from what you would get in an off-the-shelf SSD.