I looked into this angle recently. The SSDs in the new MBPs are roughly 3x as fast as the one in my 2015 MBP (7.4GB/s vs 2GB/s). To contextualize, the new MBPs have roughly half as much SSD bandwidth as my MBP does memory bandwidth.
Which is to say the SSD is much closer to being as fast as RAM, which would explain why is subjectively can make better use of less memory.
It’s also possible that they’re using more and better tricks from iOS to handle memory - in which case the Intel Macs might show similar results if given similar speed disks
Which is to say the SSD is much closer to being as fast as RAM, which would explain why is subjectively can make better use of less memory.