I keep hearing that, but I also keep running into a LOT of people who cannot resolve the failure for the 1000 series cards, and I would assume the 2000 series as well, to be recognized and provide even basic display functions on older motherboards that are at least a generation removed from the change to full UEFI firmware.
I've seen at least twenty to thirty instances where no current enough bios version was ever released to support the architecture/series or for whatever reason, they simply won't work even with full bios resets using the battery method and breadboarding techniques. Without hardware level firmware support, some of those old boards wouldn't even support some of the newer (But now old) cards prior to these mainly UEFI cards.
I'd like to agree, because I've seen SOME of them work on very old boards. But I've also seen a lot of them that haven't, even on boards that weren't as old. Much probably depends on the manufacturer and whether it was an OEM board or not too. Most of the OEM boards have never received any updated bios through the years, and those are very unlikely to work with the newest cards, or at least less likely than with an aftermarket card from one of the four main brands.
I don't even think that, in those cases where they won't work, it's a UEFI vs non-UEFI problem, per se, at least in all cases. I think it's simply a lack of support compatibility due to old firmware that doesn't have hardware level support for even newer PCI 3.0 non-UEFI architecture in some cases. That's the only reason I can think of but then again I am not a hardware engineer. There are a few guys around here who could probably answer the "why's" more directly than me. InvalidError and a couple other engineer types likely can explain exactly why.