Since GFXbench may be the Metal test that is the most favorable to Apple GPUs, I'm not sure how Apple could determine that the M1 Max was about as fast as the mobile 3080. I except it to be at least 30% slower in other tests.
And why is the M1 Max not 4x faster than the M1? It seems that everything is at least 4x better. It even has 6x the memory bandwidth. Are results constrained by latency or something?
I think the reality is that while it's nice to have these leaks to drive discussion, the reality is, they're just that. Leaks. We don't know who did the benchmarking, the conditions under which they were run, whether the silicon was preproduction or "retail," if they used the 24C or 32C M1 Max, or even how accurate (if at all) these leaks really are.
We ALSO don't know what software Apple used to conduct its own benchmarking, making comparison to these leaks, even if the leaks are 100% accurate, somewhat dubious at best.
What we do know is: Apple was confident enough in the M1 Max to not only compare it to the 3080m but to compare it against three different laptops featuring the 3080m, provide relatively detailed (for Apple) footnotes, and to compare it against multiple different TDP configurations of said 3080m.
This isn't to say Apple isn't putting its own silicon in the best possible light. I'm absolutely sure it is. But a less confident Apple would not have given that much detail. They would've just compared against one ambiguous "high end PC laptop" without giving any details. Or they would've compared provided numbers to a generic 3070m/3080m without detailing the specific laptops /TDP configurations they were comparing against.
Now, i'm not saying this means we should take Apple's claims at face value, or that M1 Max will equal/come close to the 3080m in every, or even a majority of software. Merely that, i've watched Apple for... two decades (?) or so now. I've almost never seen them provide this level of detail on the competing products they reference. They clearly feel confident so I think the best (albeit perhaps unsatisfying) answer to your question is; we're just going to have to wait for detailed benchmarking from reputable outlets after the embargo is lifted.