Wrt joining other tech companies, it is debatable whether she could get a CEO role of $30B+ tech company given she never had such an accreditation before.
Wrt your excuses on why she failed, those are exactly that - excuses. If it is such a common knowledge that middle managers are political centers, why didn't she do anything about it? There wasn't a single round of layoffs at Yahoo in her first 2.5 yrs when everyone was asking why Yahoo needs 12k+ employees to support $4B in annual revenues. She failed to figure out what was wrong with Yahoo and take adequate steps to fix it. In essence she completely failed in her duties as ceos.
I think a lot of frustration here is not that CEOs earn that much. I, for one, am totally fine if Satya Nadella earns $100M+ for all the great work and transformation he has done over at Microsoft. So I don't agree with your proposal on fixing the salaries of CEOs based on a multiple. I think what is frustrating here is that here is a CEO who clearly failed across the board and did nothing noteworthy (and made huge costly mistakes such as hiring Henrique de Castro which cost Yahoo $100M) but still was seemingly unaffected in securing the CEO role and being paid handsome salary/bonuses.