"another worried about the ability of managers to stanch the flow of valued employees."

That is the problem right there: shitty managers at Yahoo. I spent a few years there, and despite being in the industry for many years, I've yet to find a more dysfunctional setup. Managers have absolutely zero accountability at Yahoo. In any other place, if engineers start leaving a manager, it would be cause for concern; if too many do so, the manager is axed. But in Yahoo, shitty managers hang around, hopping from project to project, biding their time till they can find a new project to shit on.

And the tech stack?!? Don't even get me started.

Yahoo needs to cut out its management layers, and reduce the manager headcount by 75%. Only then will it start turning around.