Earlier quoted context omitted.
What I'm reading here is that even as an experienced interviewer you struggle to make the format effective and equitable. Sounds to me like the format isn't worth keeping; time to hire more, and fire fast?
Hire fast and fire requires even more effort and commitment from a candidate, I’m not sure how that would be an improvement. Firing fast would be like 3 months of interviews! I’d also like to add that having multiple interviewers, if they have diverse backgrounds, is more likely to be equitable than a single interviewer.
If employers with lengthy interviews want to pay people for their time that would be fair.