I agree, the comparison with CRAM is in the whitepaper of MPEG-G. But the author of the blog has some more recent posts, where he is very skeptical of the claims made with respect to the CRAM format. It's worth the read.
There are no "comparisons with" CRAM in the MPEG-G preprint, only comparison between CRAM and DeeZ, taken from the DeeZ paper. Those comparisons are fair and correct, but obviously were done at the time that paper was written - some 4 years ago. Since then CRAM has moved on (as has deez), but modern CRAM generally beats modern DeeZ if we restrict ourselves to the formats that permit random access (DeeZ has a higher compression non-random access mode).
So far there have been no direct data on how well MPEG-G does bar an old slide from a year ago; ISMB talk I think.
From that we can glean some compression ratios at least. I attempted to compress the same data set with CRAM, but that data set, while public, is in FASTQ format instead of BAM. I asked for author of the talk how he had produced the BAM, but got no response. I tried my best stab at creating something similar, but it's not a satisfactory comparison yet.
