Your hung up on the compression arguements I think, Ps5 also has the old method as well, and they can do RDO on data before storage if they wish, so same as BCpack. Also does not take into account SPEED of decompression.
The 5.5 and 2.4 is the rough raw speeds stated....not accounting for latency, and given the 3 x more data lanes for Ps5 and similar chip speeds...I think the 5,5 is lowballing (under stated) so Sony say the off teh shelf expansion is maybe OK if you remember Sony speech,
If sony said hey it does 12 all the time, no you cant buy an expansion same speed from anyone else........Hence the low ball / understated numbers....IMO
The 8-9 and whatever are meaningless chosen probable specs, the max of 6.5 and 22 are very interesting, says allot...
If it was RAM and you had a 12 vs 4 lane bus and same speed chips, what would you think was bandwidth ratio ?