It’s just a completely different test. GB5 multicore afaik was executing a process on each core in a parallel way. GB6 is doing something closer to concurrent operations which probably resemble something like X amount of threads processing data from a channel with a mutex.
If that's the case, GB6 multicore (which shows the Ultra chips and the M3 Max as EXTREMELY powerful - right up there with very big Windows workstations) is probably closer to the truth in an average workstation use case than GB5 multicore, which sounds like it almost requires a multi-user system to generate enough independent threads. A GB5 benchmark sounds closer to accurate for a VAX from 30 or 40 years ago, when you might have had 100 people logged in at once, using text editors and checking e-mail. 100 copies of emacs is a much easier test for a many-core system than one copy of Photoshop...
If schedulers are that bad at using 50+ cores, then the M-series chips have a huge advantage at classic workstation tasks. An M3 Ultra should easily beat even a Threadripper Pro 7995WX at a GB6-like task mix (let's see if that's true on something like a fully non-Rosetta PugetBench). To be fair, all the Xeons and Threadrippers are really server chips - they are designed for workloads that are actually closer to that old VAX - a million little tasks rather than a few big ones...
Even if GB6 is unrealistically optimistic, and real-world creative tasks show it as close to the big Threadripper, but not ahead, remember just how huge a difference there is between the systems in price and livability.
An M3 Ultra is going to start at $4000-5000, and it'll go up to $10,000 or so with high RAM and storage - maybe $12,000 if Apple has some monster options. A full 256 GB of RAM, but with somewhat modest storage (2TB) should be around $7000. Add external SSD storage for a few hundred to a few thousand more (depending on your needs). I wish Apple offered add-it-yourself NVMe, but they don't... $10,000 buys a heck of a system.
$10,000 buys a Threadripper Pro 7995 WX, too - a bare CPU. Building a decent workstation around it is going to be right around $20,000. Maybe less if your work isn't RAM or storage intensive (. Maybe more for super configurations (that the Mac Studio may not be able to match). Just adding up the parts, it's really expensive
CPU: $10000
Motherboard: $1000 (conservative estimate - these aren't out yet, previous generation is $1000)
Case, PSU, cooling: $1000+
GPU:$2000
RAM: $1000 for 256 GB
Storage: as desired (2 TB is only a couple of hundred dollars)
Where the Mac is probably going to be about $7000 with 256 Gb of RAM and a 2 TB system/application drive, a 7995WX will be about $15000 in the same state.
A M3 Extreme (double M3 Ultra) Mac Pro (if such a thing ever exists) will compete with the big Threadripper on price, and if GB6 is correct, may well be twice as fast for tasks that don't love 96 cores...