Look at Google as an example. Google started as a search engine and ad company, and has since reinvented itself with investment in new areas like photos, email, Android, etc.

Yahoo started as a search engine, ad company, 'portal start page', and email. They kept doing the same old thing and went nowhere.

But they still had products with value- Flickr for example. Managing photos was starting to become a big thing, but they let Flickr stagnate, it got no development, and eventually people stopped using it. Look at their email product as another- Gmail focused on making their email usable, clean, fast, great storage, and without lock-in. Yahoo email sucked and it was hard to get rid of them because for a long time they didn't support IMAP (what you'd use to vacuum out your old messages) or email forwarding. People stayed not because it was a great product, but because they were stuck. But that's a real missed opportunity- Yahoo Mail could have been what Gmail became.

When Google modernized their site with web 2.0 technologies like AJAX and updated the look and feel to match, Yahoo still felt like a Web 1.0 site with ads all over the place and messy design.

That's why I say she ran the company into the ground. Just because Yahoo wasn't leading the pack when she joined doesn't mean there weren't any wins to be had. It's the job of CEO to recognize where the company should invest and innovate and where they should stay the course.

Another example- one of her big decisions was ending all remote work for Yahoo employees, without consideration for employees that didn't live near a Yahoo office, or even how much office space Yahoo had. I remember reports of people working in hallways and sitting on the floor because there weren't enough desks for everybody that was forced to come in.

To be clear- I'm NOT saying she's stupid. She's obviously very smart. But I am saying she wasn't a good leader, and made many decisions that were obviously wrong both at the time and as seen historically. She does not seem to be a person with good business sense or the right kind of leadership, for a great many reasons.