PhD is doing something very niche, intelligence and logical thinking makes it easier, but you can easily just submit a paper in multiple journals until one accepts. Of course your advisor and committee are supposed to weed out those people, but in this culture where more students graduated -> faster tenure +more funding, and everything is measured in numbers, everyone is encouraged to increase the numbers instead of quality. So just because you were able to publish something in a small niche field doesn't mean you know a lot about the world, or you agree with what other scientists think.
I know different universities and countries have their own system which probably have higher quality control, but this publish and perish culture combined with the competitiveness and lots of money involved in all steps is bound to game the system towards anti-science. Professors don't really have the luxury of trying things that don't work for years anymore.
Well sometimes when you are a tenured professor, it's really hard to mess up in many cases. I personally know professors that have "gone senile" to put it mildly, if not then it just means they were stupid from the start. That have ridden their one good discovery from decades ago, and can keep getting funding because other orgs are also funding them. Have way too many students than they can handle in their lab, make postdocs do the management, and fire people if they don't publish well. Of course that's the only example I have seen of someone that incompetent. But I have seen mildly incompetent people riding on "collaboration" with other labs and people from university, or by being "cheaper to hire than consultants". Academia in US is a lot like a boy's club of who knows who. And once you have a certain momentum you'll have funds that can support more people than you can manage while new professors will struggle with getting funding and have to use those old professors to get funds and "collaborate" with them. Basically giving away a chunk of funding for their names.