The problem was specifically DoubleClick management, who then got inserted in high levels within the Ads organization, forcing out the very technically & economically savvy people who were there before.
This is a recurring problem in large organizations. People who spend their time learning to be politically savvy will be...politically savvy, and be at an advantage when playing power politics that determines who is in charge. The effort needed to become politically savvy usually comes at the expense of domain/technical/economic knowledge required to actually get the job done. Eventually the organization becomes very good at playing political games and very bad at getting stuff done, until it collapses.
YouTube has obviously done well, but look at everything they’ve done since the ad sales mentality dominated their thinking. Stuff like Google+ happens when you are thinking “we need X to keep Facebook from cutting into our ad revenue, therefore our users will use X” rather than asking “what will our users like more than Facebook?”.
The other side is what we saw with things like Stadia, GCP, or G-Suite where executives used to the ad model have trouble with other business models. The problem there again isn’t that ads are evil but rather that you need to understand your users and what they want so you can think about the product the right way.
There's a long list of companies that died by being acquired into a bad culture. OP is talking about the opposite: an acquisition so toxic it rots the parent company.
Netscape died because Microsoft bundled their browser with the operating system and made it free for commercial use, what essentially led to the huge antitrust case.
Only after that did browsers become utilities in the OS, with open source engines like Konqueror's KHTML (which later became WebKit, which later became Blink) and Netscape/Mozilla's Gecko