Alan Kaye unfortunately is a big part of the problem. Mattel HR enables the worst in Mattel and allows mediocre to poor to survive and thrive. Moving people around if they've failed for several years in a group isn't a solution - it's deferring what needs to be done. TRACs? CAP? All of those tools are useless. If Sinclair really wants to change Mattel, he needs to start by firing Alan Kaye and most of his HR chronies and get a real HR team in that understands what's needed - and when managers have streams of people quitting on them, takes action and removes that person (looking at you, NAD) vs. ignoring the problem. Part of HR is firing people that aren't cutting it, are detrimental to a company, or can't move to the next level. Instead, HR moves the problem to other groups. That's not HR, that's passing the buck.
If Sinclair really wants to make a positive step, bring in HR from outside and clean Alan's house. It's the only way you can change the culture, which is what is most critical for Mattel to make the changes it needs.