[SPOILERS] I don't buy the "Kier Eagan" theories

Made the title vague to avoid possible spoilers.

I see a lot of the theory that Lumon wants to revive Kier, and also similar theories about the Board being some composite hivemind of dead CEOs, or that they're all living in a chip in Natalie or the current CEO's head. But it doesn't make sense to me. Most of these people died way before there could have been any severance-adjacent technology. Kier has probably been dead since the late 1800s, so IMO it's not even plausible for his brain to be cryogenically frozen or anything like that. So what could they have used to revive him?

At most, Lumon could be molding someone's brain into a version of what they imagine Kier was like when he was alive, and deluding themselves into believing it was the original. Possible, since they are a deranged cult, but I don't think it's a satisfying answer for the whole mystery of the series.

I also think narratively, the writers wouldn't go for a dead CEO hivemind without having Kier involved. He's the only one we ever hear about. If the grand reveal was "Dead Eagan CEOs #6-8 are living on inside a severance chip", it's not that interesting in comparison.

Curious what other people think!