I apologize. This was just me being stupid. I absent-mindedly picked up the Minion of Chaos earring from DSH at level 76, and was so used to using my broom, that I thought the broom was focusing the 76 pet -- completely forgetting that I had a new, better focus earring. MoE does, indeed, only ...

Minion of Eternity focuses until L80. I know this, because at L76 and 77, I am getting improved pet base hits, when I wield The Sweeper.

It is, by far, the easiest focus to obtain that works to 80, unless your toon is part of a guild that routinely has older content raid drops of the better foci ...