Having worked at four companies I have yet to see there being any serious discussions on merits of which questions to ask, the style of interview to be conducted, how to grade candidates reliably, or the amount of help and guidance to give candidates. In short as far as I can tell the whole tech interview process is generally a mess.
I have tried to push for discussions on all of the topics above and most engineers simply do not find the topic interesting enough to engage at length. There's a lot to discuss and everyone complains about the current state of the interview process across the whole field yet few do more than complain. Alas that is life.
As for vetting for "positive-only", I am not sure that's something that can even be done. Usually conducting interviews is part of your performance and you are expected to do them or it will reflect poorly on you as an employee. So every senior engineer or above typically will aim to do some amount of interviews and, let's say you are one of them and you are not very happy, when you get asked by your manager whether you are a positive employee, you are very unlikely to say no.
Also unhappiness is a pervasive quality regardless of title and you can very easily find high level managers and one year out of college engineers that are equally unhappy if you were to ask them candidly. This is a separate topic, but we as an industry have potential to make our workplaces incredibly engaging and rewarding but that potential somehow seems so very hard to achieve.
Whoa! Really?!?!?!
That's a huge difference from any of the places I have worked. If you didn't want to be on the interview loop, nobody in their right mind thought it would be a good idea to command you to do so.
Normally people wanted to be on the interview loop simply so they had input on the people who might become their colleagues. But there were people who wanted nothing to do with the loop and that was okay, too. Maybe you simply had too many deadlines or just were an introverted personality.
But forcing people to do the interview loop? That's seems like a recipe for disaster.
Interviewing is apparently the most popular choice to fulfill this requirement, so get ready for a glut of disinterested people interviewing you at google.
The fact that someone in the interview chain is willing to tell you significant negative information dramatically raises the Bayesian prior.
An interview chain is normally extremely well vetted for people who are positive-only. The fact that this failed is a dramatic cause for concern.