What we had with two PCIe power connectors was 12 large pins delivering 300W. That's 50W per circuit and 4.17A per wire.
12VHPWR also has 12 pins, so for the same safety margin as PCIe it would be a 300W connector with no more than 50W per circuit and no more than 4.17A per pin.
Except they also made the pins smaller, so we know that its less safe then 2x 8-pin because laws of physics apply - specifically Joule's first law and Ohm's law. This is grade school stuff, nothing complicated.
Doing some napkin math on the mating area of the two connectors, I'm going to ballpark Amphenol's Minitek interface current-handling capability at about 75% of Molex's MiniFit Jr's. The the total contact surface area of each pin/barrel interface seems to be about half but Amphenol have done some flexing beam thing rather than dimples to provide contact force so let's give them some margin back. However, the change from dimples to flexing beam is unlikely to really account for the overly-generous gain I'm giving it since ECR (electrical contact resistance) is usually so negligible that it's difficult to measure and can be practically ignored as other resistivity factors scale faster with current and temperature. There's no getting around the obvious fact that smaller pins simply have less contact surface to carry current.
Using that rather generous 75% capability value, the Amphenol Minitek power connector at 75% of MiniFit Jr's 300W is a 225W connector. I don't care if Amphenol say it's rated for 9.5A per pin, it's a significant downgrade from MiniFit Jr. and looks closer to 2.5A per pin to me. At just 6.25A per pin (so 450W as per the connector rating) it's already being asked to do double what we've been calling "safe" for the last 20 years.
I'm not against a new connector. Using 4x 8-pin is pretty silly for these behemoth 600W GPUs, but at the same time, I'd like it to be better, more reliable, and safer (or at least as safe) than our existing PCIe standard. There are so many wasted pins in multiple PCIe connectors and quite honestly the 450W GPUs in question have no shortage of physical space to accommodate something larger than 12VHPWR.