Some comments:
1. If you're a bootcamp grad, be aware that impostor syndrome / low confidence / "maybe I'll be ready to interview after I take one more class" is a FAR GREATER RISK than not knowing big o. When you read an essay like this, consider it as useful input. Big O is useful, and is a special point of interest to interviewers, but do NOT listen to any of the voices (especially those in your head) telling you "you're not a real engineer until you XYZ". So, by all means, internalize this essay if your takeaway is "nudge big o up on the study list". Reject this essay and everything it stands for if your takeaway is "I am not ready to be a software engineer yet".
2. A dissenting viewpoint from me: this is good advice for interviewees, but interviewer focus on Big O / data structures / etc is a part of the same culture that fetishizes CS degrees from tier-1 schools and mistakenly believes that the most difficult/valuable part of software engineering is computer science. In reality, the most difficult/valuable parts of software engineering are craftsmanship (measured in decades of real work, not built at schools except those named waterloo) and working effectively in teams. Big O is not uniquely useful to your work or uniquely difficult to learn on-the-job. You should study it anyway because many interviewers believe that it is.