The ones with the best data are the company themselves, especially those who interview thousands of candidates a year. These companies (e.g., all FANG) have enough data to assess which interviewer, which interview questions and which interview process have positive correlation (and even causation) with future employee performance. And they can optimize the pipeline to interview most candidates with the interviewers that can actually assess future employee performance for instance.
Either these companies have already done these optimizations and analyze the trove of data they have, and the process is what it is for a reason. Or they haven't yet and there is still much room to optimize the process, and applicants have a chance to see those processes updated for the better (although here better means better for the company, not necessarily better for the applicant).