If ass covering is easy like that, what’s actually the argument for insane leadership comps?

There is no argument for it if the company is a legacy juggernaut with basically zero new product development (which is most of the Fortune 500).

Leadership comp is a total grift and has ballooned in recent decades (in the US exclusively) since the 1980s due to the shift to stock-based comp. Fun story, a lot of analysts didn’t even count stock based comp as part of the cost structure of a company until oddly recently.