You sound like someone who has never been a manager or has no idea what a manager does.
Yes, you're right that defects are made by developers. But you'd be hard pressed to find an example of a software defect that destroyed a company. Even if you as a DevOps engineer cause your company to be down for a day, it probably would have little effect on your company's bottom line.
I was in charge of Reliability for Netflix. Our whole site was down for Christmas Day one year. No one was fired, and it barely affected anything. That was a pretty major defect.
However, the way that management handled that outage had a huge effect on the company surviving that incident. Making sure we focused on the right problems to solve to prevent it from happening again. Creating entire new groups of engineers and then hiring them to solve specific problems of moving traffic between regions.
So yeah, management is really important, and a good manager is definitely more effective than a single engineer. And management decisions can destroy a company, but I doubt you can find even one example of a single engineer's decision that took down a company.