On the contrary, log4j incident is an excellent example of how relying on open source for security completely failed. This vuln existed for years, all while being open to security researchers to find it. They didn't. Instead, there is evidence that black hats found the vuln first (perhaps because log4j is open source?).
Please, let's continue this back-and-forth of condescension. It's really productive. /s
Maybe it's not, maybe you guys have drastically improved things. What makes me strongly doubt it is that we still haven't seen substantial liability or other consequences for bad or negligent actors in this space.
FAANG security is just like everywhere else: mixed. There are mixed levels of knowledge & experience, and mixed views: i.e. even though there's a lot of consensus on high-level tenets and frameworks, like e.g. Google's Beyondcorp stuff (along with some certain security 101 stuff that's been discussed for the past 138 years), you'll always get engineers who don't like X or Y. Just like anywhere else.
Nothing is a continuum.