Priors and bias is exactly why you want MORE interviewers though.
"Drawing out the interview process is a thinly veiled attempt to launder this bias with a "neutral" process that they will likely disregard/overrule if it contradicts their personal preference.
That doesn't mean that I think this sort of interviewing bias is good or acceptable, but I also don't think drawing out the interviewing process corrects for this bias either."
I do agree about the "you only need 15 minutes" part, but the solution there would seem to be replacing four hour long interviews with four 15 minute interviews, rather than with 1 hour long interview.
Where do you get the varied interviewers really? Is it from the same biased hiring process?
People who haven't build sustainable, profitable organizations typically have no clue about hiring. Sure, they may be able to hire well for their little project. But, if you care about the culture of the company and how you want to shape it, you almost want all of your current members to have a say in the new member
For most companies, including Google as a more mature company, the dynamics are different. You might be quite happy to hire candidates who weren't top of their class but who are going to be easy to work with and get stuff done. And you want to make very sure you don't either reject or turn off the (maybe small number of) outstanding performers who want to work for you.
Google IMHO completely fail at the latter these days. A solid A student who knows how to present themself and really wants to work at Google will be hired. A genius with an unconventional educational background probably won't be.