My tired-ass brain realized this.

Mondas and Shiver Star...

Specifically the Cybermen. While Simm’s Master does have a final plot involving Cybermen he’s not really in control, he has influence but is not in charge and by the end is “on the menu”.

Dahwan’s Master is initially not involved with the Cybermen but eventually gains control over them when he steals the Cyberium from Ashad. We don’t see him lose the Cyberium when he’s dying so presumably still has it.

Then there’s the Cybermen themselves, when we see the Cybermen initially in 13’s run they are the Cybus model and the more advanced armored models that look like a mix of Cybus armor and Modasian design.

The Cybermasters take this design and make it more Time Lord Themed. They also have the fatal flaw that they have a finite amount of convertible bodies as the Time Lords are already dead and no new ones are being born.

11 & 12’s era’s Cybermen have a more streamlined design & incorporate flight into their capabilities which I think might imply that these are the later designs from after the Cybermen have run out of Time Lord bodies to upgrade and gone back to upgrading humans.

The have also learned to convert the dead into Cybermen, something that they didn’t seem inclined to do to the humans they killed in Ascension of the Cybermen, they however do this with the dead Time Lord bodies after The Master has the Cyberium, possibly indicating that this is something he taught them to do.

I also believe that Missy might have removed the Cyberium from herself and put it into the bracelet that she uses to control the Cybermen.

Like I said, this is just my theory on the timeline. Which I think enhances the Storyline rather than erasing Missy’s character Arc.