Regarding the core business, we're in an era where markets are becoming more winner-take-all meaning scale is your network effect and there are huge gaps between 2nd or 3rd place and the rest. This is especially true in ad tech and ad supported businesses (Facebook, Google, and the rest). From this perspective, Yahoo core is probably hugely more valuable to Verizon or another massive company who can credibly challenge Facebook and Google, than it would be by itself.
The reason the market values Core Yahoo negative, is because it thinks the current management will destroy capital by spending it on useless acquisitions and costly R&D to become a growth company again.
But accepting that it is a stable company that's going to bring in billions in revenue for years, and just milking it dry is actually not a bad strategy. It's a very boring strategy though.
A Yahoo with a declining profit margin and market share is worth less in terms of any likely future dividend. So the share price drops accordingly. Normally, this would make it more likely for an outsider to purchase the company as those that bought at the higher price would be willing to see either a small loss or a small profit (depending on when they bought) and close out their position. The purchaser could then sell the pieces or merge with another company or do something to get more revenue later on.
What complicates all this is the shares that Yahoo has in BABA and Yahoo Japan, which set a hard floor on the stock price (and lowers the potential upside for any acquisition, making it hard to find buyers for the whole company). However, they can't just sell out of those positions and pay off some existing investors and/or buy shares, as they would have to pay a hefty tax fee and probably tank the stock price as it tried to find a new floor.
One potential way out of this would be to find a way to kickstart the company growth so it would be valuable enough that investors would hang onto it. That hasn't worked. Another way is to try and just spin off the BABA shares into another company, give those to some investors so they can close out their positions with a profit, and the remaining investors can focus on the business. That got nixxed by the IRS.
So they're basically stuck doing the same chop shop deal that a "corporate raider" might pull, only while taking a huge PR hit and a hit to morale because they're supposed to be the "good guys". Not some "outsider" pulling a hostile takeover.
Yahoo has plenty of smart people itching to do the right thing.
She was not a destroyer who came in to trim down to the appropriate level, she was the creator expected to raise them to new heights with all kinds of new ventures and projects.