I think it's possible NV went for a cheap(er) design for reference PCBs, which is normal, and there aren't enough phases to handle all the current. There is an issue with New World not respecting power limits (set it to 100% which is, let's say 375w, and yet the game will stay pegged at 400w). Games should not be able to do that outside of super hard transient loads that the VRM can't keep up with, which is acceptable. There needs to be an implementation from NV on the driver side to stop what New World is somehow doing.
Yes, all reference boards are using UP9511s for the vCore VRM. If the VRM is the issue then it would affect pretty much any card using the reference design. This explains why the FTW3 is also having issues despite being a custom PCB - it's using UP9511s.