Question about Atium/Nalatium

It's been a minute since I've read mistborn so please correct me if I'm wrong about anything.

Originally Preservation's plan to stop Ruin was to create people who could burn his body (atium) and stop him from reaching his full power. I believe in a WoB from 2009 he mentioned that Preservation swapped out cadmium and bendaloy for atium and malatium to make this happen.

However, in 2021 Brandon changed it so that the atium we see in Era 1 is actually an atium-electrum alloy and the atium mistings from Elend's army are actually just electrum mistings. He made this change I think because he thought Atium should be burnable by anybody like Lerasium and other God metals are.

Doesn't that undermine the point of Preservation's plan? Was his plan actually to dilute all of the atium with electrum?

Also smaller question but what of the 1/16 of the people that got snapped by the mists? Does that mean electrum mistings are the most powerful since they took the longest to recover? Were there cadmium and bendaloy mistings that got snapped and never figured out their metal?

Please let me know if I am wrong about any of this, I've just been fascinated by the atium retcon recently.